Cummins isx12 g level 1-source_file_092514

Technical Resource Guide
Cummins ISX12-G
Fuel Systems
Level One

ISX12-G Fuel SystemsRevision 1
October 1, 2014
This material is based upon work supported by the
California Energy Commission under Grant No. 12-041-008
Project Director/Editor
Cal Macy
Development team of Subject Matter Experts
Cal Macy
Bob Vannix
Rich Mensel
Pete Sparks
Photography
Cal Macy
Bob Vannix
Doing what matters for jobs and the economy with funding provided by the
California Energy Commission (senate bill AB118) through a partnership
with the California Community Colleges, Ofﬁ ce of Workforce Development,
Advanced Transportation and Renewable Energy sector.
Created by: Long Beach City College Advanced Transportation Technology Center 1305 E. Paciﬁ c Coast Highway Long Beach, CA 90806 562-938-3067 http://www.lbcc.edu/attc/ [email protected]

1ISX12-G Fuel Systems
COURSE INTRODUCTION
Course Title
ISX 12 G Level 1 Training
Course Length
16 hours
Description
This course is designed to give technicians the hands-
on skills needed to diagnose and repair the 11.9L
Cummins ISX12G NG fuel system. This course
covers sensors, actuators, pin-out voltage values and
real world diagnostic applications using Cummins
Electronic Service Tools. This course includes the
discussion of:
▪▪Fuel system components
▪▪Identifying the flow of air, fuel, and EGR gasses
▪▪Defining and contrasting Mass Air Flow Fuel
Management Systems
▪▪Speed Density Fuel Management Systems
▪▪Identifying, locating and testing parameters with a
DVOM
▪▪Temperature Sensors
▪▪Pressure Sensors
▪▪Position Sensors
▪▪Voltage Producing Sensors
▪▪Mass Gas & Air Flow Sensors
▪▪Using INSITE™ to verify parameters
Course Benefits
Students receive a wealth of experience working on the
system and understanding where everything is located
and how it works. This class is a must for technicians
involved with diagnosis and repair of natural gas engine
management and fuel delivery systems. Students will
learn the proper and safe methods of working with
the high pressure CNG fuel systems as well as LNG
cryogenic fuel using DVOMs and the laptop diagnostic
software specific to the Cummins controllers.
Reference Material installed on technician-provided
USB drive upon completion of Levels One & Two.
Prerequisites
Familiarity with DVOM, Electrical I and engine fuel
systems.
Objectives
▪▪Define Speed Density Fuel Management Systems
▪▪Define Mass Air Flow Fuel Management Systems
▪▪Identify and Examine the various systems
▪▪Identify and test sensors and actuators with a DVOM
▪▪Use INSITE™ to verify parameters
Competence:
Competence will be measured by both lab
demonstrations and class participation.

2ISX12-G Fuel Systems
Course Introduction
Instructional Objectives
By the end of this course, the student will be able to:
▪▪Define Speed Density Fuel Management Systems
▪▪Define Mass Air Flow Fuel Management Systems
▪▪Identify and Examine the various systems
▪▪Identify and Test Sensors and Actuators with a
DVOM
▪▪Use INSITE™ to Verify Parameters
Important
The Material presented here is intended for
instructional purposes only. Please be sure to follow
manufacturer’s latest bulletins and procedures as the
ultimate source.
Agenda
▪▪Specifications and Power Options
▪▪Maintenance Schedule
▪▪Component Identification & Location
▪▪Natural Gas Flow & Components
▪▪Air Flow & Components
▪▪Exhaust Flow & Components
▪▪EGR Flow & Components
▪▪Actuators, Solenoids, Switches & Misc. Signals

3ISX12-G Fuel Systems
Course Introduction
Pretest
Cummins ISX 12-G Fuel Safety
Level One
1. The Cummins ISX 12L engine can only run on CNG and not LNG? (T/F)
2. A Fuel Control Valve is similar to a fuel injector? (T/F)
3. The Cummins ISX engine is a Speed Density system versus a Mass Air Flow System like
the 8.9L ISL-G? (T/F)
4. The EGR Valve has only two positions? (T/F)
5. The Cummins ISX 12L engine has a knock sensor for each cylinder? (T/F)
6. What best describes best practice for replacing spark plugs in a Cummins ISX engine?
a. Clean the old dielectric grease from the spring connection with a lint-free cloth
b Wipe the ceramic portions of the spark plug with alcohol after handling
c. Replace the rubber boot with a new one included when buying spark plugs
d. All of these are considered best practices for replacing a spark plug

4ISX12-G Fuel Systems
Introduction
▪▪Pretest
1. Engine Orientation
▪▪ISX12-G Specifications
▪▪Engine Power Options
▪▪Maintenance
▪▪Theory of Operation
▪▪Mass Air Flow System
▪▪Speed Density System
▪▪Engine Component Overview
▪▪Activity 1.1

2. Chassis Fuel Flow
CNG/LNG
▪▪Fuel Flow Overview
▪▪CNG Fuel Flow
▪▪LNG Fuel Flow
▪▪CNG Storage
▪▪LNG Storage
▪▪CNG/LNG Common Components
▪▪Natural Gas Fuel Flow
▪▪Natural Gas Fuel Filters
3. Engine Fuel Flow System
▪▪Low Pressure Fuel Regulator
Assembly
▪▪Low Pressure Regulator
▪▪Low Pressure Shut Off Valve
▪▪Fuel Pressure Sensor
▪▪Wastegate Control Valve
▪▪Natural Gas Fuel Flow
▪▪Fuel Control Module
▪▪Fuel Control Housing
▪▪Fuel Control Venturi
Table of Contents
▪▪Mass Gas Flow Sensor
▪▪Fuel Control Valve
▪▪Natural Gas Fuel Flow
4. Engine Air Flow System
▪▪Air Flow Overview
▪▪Compressor Inlet Temperature,
Pressure & Humidity Sensor
▪▪Turbocharger Compressor
▪▪Air Charge Cooler
▪▪Throttle Inlet Housing
▪▪Mixer Intake Pressure Sensor
▪▪Throttle Actuator
▪▪Throttle Plate Position Sensors 1 & 2
▪▪Mixer Assembly
▪▪Activity 1.2
▪▪Intake Manifold Pressure/Temperature
Sensor
▪▪Temperature Sensors
▪▪Measuring Voltage
▪▪Testing Temperature Sensors
▪▪Pressure Sensors
▪▪Testing Pressure Sensors
▪▪Activity 1.3
5. Exhaust Gas System
▪▪Exhaust Gas Flow Overview
▪▪Turbine Inlet Temperature Sensor
▪▪ECM uses the Turbine ITS
▪▪Turbine Inlet Temperature Sensor
Testing
▪▪Catalyst Inlet Oxygen Sensor
▪▪Testing Heated Oxygen Sensors
▪▪Catalyst Temperature Sensor
▪▪Catalyst Outlet Oxygen Sensor
▪▪Activity 1.4

5ISX12-G Fuel Systems
▪▪Exhaust Gas Flow Overview
▪▪EGR Cooler
▪▪EGR Temperature Sensors
▪▪Electronic EGR Valve
▪▪EGR Position Sensors
▪▪EGR Delta Pressure Sensor
▪▪Activity 1.5
6. Base Engine Sensors
▪▪Engine Coolant Temperature Sensor
▪▪Engine Crankcase Pressure Sensor
▪▪Engine Oil Pressure Sensor
▪▪Engine Oil Temperature Sensor
▪▪Speed Sensor Types
▪▪Camshaft Speed/Position Sensor
▪▪Crankshaft Speed/Position Sensor
▪▪Electronic Control Module
▪▪OEM Installed Sensors
▪▪Vehicle Speed Sensor
▪▪Accelerator Pedal Sensors
▪▪Remote Accelerator Pedal Assembly
▪▪Activity 1.6
▪▪Coolant Level Sensor
▪▪Switched ECM Inputs
▪▪Warning and Indicator Lamps
▪▪Data and Control Signals
▪▪CAN, J1939, J1587 Data Bus
7. Ignition System Component
▪▪Ignition System Components
▪▪Combustion Knock Sensors 1 & 2
▪▪Combustion Knock Sensor 1
▪▪Combustion Knock Sensors 2
▪▪Combustion Knock Control Systems
▪▪ICM Spark Voltage & Misfire Signals
▪▪Coil on Plug Ignition
▪▪Activity 1.7
Post Test
Natural Gas Safety
Considerations
References

6 ISX12-G Fuel Systems
Module One
1

7ISX12-G Fuel Systems
ISX12-G Specifications
The ISX12G CM2180A is spark-ignited, turbo-
charged, natural gas engine based on the 11.9 liter
diesel automotive (ISX12G) platform and shares
many installation options with the diesel counterpart.
The engine is run on low pressure natural gas
that can be stored as Compressed Natural Gas,
Liquefied Natural Gas or Bio Methane. Each fuel
is transformed into low pressure natural gas to be
introduced to the engine.
The ISX12G engines will use stoichiometric
combustion technology to enable a three-
way catalyst after-treatment. While running
stoichiometric, the system must run evenly between
rich to reduce NOx using CO (to react with the
Rhodium in the front of the cat) and lean to absorb
oxygen (in the platinum and palladium of the rear
section) to oxidize/burn the HC/CO. This replaces
the lean-burn technology of the previous C Gas Plus
and L Gas Plus. To do this, in closed loop the ECM
utilizes oxygen content readings from the oxygen
sensor to adjust fuel delivery and maintain as close
to stoichiometry as possible. When the ECM
ignores or doesn’t receive a signal, the computer
reverts back to a pre-programmed open loop control
strategy. This can happen in many operating modes
depending upon conditions.
This ISX engine produces output in the 400hp range.
Peak torque is 1450 ft-lb, and max RPM is 2100 rpm
governed. The ISX12G has an oil system capacity of
12 U.S. gallons and coolant capacity of 26.5 gallons.
Engine Orientation
ISX12G Engine Power Options
Available power and torque configurations
ranging from 320hp to 400hp are available from
Cummins. Customers should determine which
configuration best suits their needs. Although there
are some differences in cam timing to achieve the
higher output configurations, most differences are
calibration changes that result in the higher outputs.
It is important to remember that wear and tear
longevity as well as fuel economy suffer with the
higher output configurations.
This engine has been primarily designed for class 8
heavy-duty truck applications.

8ISX12-G Fuel Systems
Module One
ISX12G Maintenance
The recommended service intervals from Cummins
are based upon normal duty cycle average speed of
45 mph. Most fleets will determine their own PM
intervals and will not adversely affect the Cummins
warranty as long as the intervals do not extend
beyond these recommendations. This information is
based upon a normal duty-cycle of 45mph average
speed. Note that spark plug change intervals and
overhead adjustment would be reduced for lower
average speeds/duty cycles. One should always refer
the vehicle owner’s manual for the complete details
on each vehicle’s maintenance intervals.
Theory of Operation
This engine, unlike the ISL-G 8.9L, uses an algorithm
to calculate mass air flow based on manifold
pressures and air temperatures. The early engines in
production utilized a mass air flow sensor that were
later eliminated. Even those with the sensor had a
software recalibration that ignored the mass air flow
meter’s input.
▪▪System uses the Mass Airflow calculation and
Mass Gas measurements to determine correct
fuel delivery which is based upon present load
conditions.
▪▪Mass Air Flow measurements are obtained from
the air pressure, temperature, and engine speed
sensors
▪▪Some later production engines have eliminated
the Mass Air Flow Sensor
▪▪Stoichiometric system uses a fuel control valve
that is like one large injector to meter fuel delivery
to the mixer. An oxygen sensor then monitors fuel
trim/air/fuel mixture and in turn signals the ECM
to make corrections as needed.
The control system for this engine is a closed loop
control system. The CM2180A ECM determines the
amount of fuel being delivered by the fuel control
valve and controls the throttle plate position and
fuel control valve open time to provide the correct
air:fuel ratio based upon driver and vehicle demands.
In addition, the ECM monitors use the gas mass
flow sensor to compare the actual fuel flow to the
commanded fuel flow to compensate for any errors.
The ECM uses preprogrammed look-up table
parameters to meet various conditions to satisfy these
engine requirements when the engine is in open-

9ISX12-G Fuel Systems
Engine Orientation
loop (engine warming up or faults codes are set) and
relies on the pre-cat O
2
sensor to provide the air-fuel
mixture update information when the engine is in
closed-loop mode. Normally, when the engine is
started, it is in open-loop mode for approximately
1½ to 2 minutes before going into closed-loop mode.
This happens each time the engine is started.
The engine uses a closed loop control system for its
operation. There are two O
2
sensors on this engine.
The Pre-Cat Oxygen sensor is located just after the
turbocharger and before the three-way Catalytic
Converter. This O
2
sensor is used to notify the
ECM of the current air-fuel mixture by its oxygen
content. The second O
2
sensor referred to as the
Post-Cat HO
2
S is located after the output of the
catalytic converter. Its only function is to monitor the
condition of the catalytic converter. It is not used to
determine the air-fuel mixture.
The first oxygen sensor’s output is used by the ECM
to verify that the fuel control valve position and
the throttle plate actuator position are providing the
desired exhaust gas condition. If the oxygen content
of the exhaust indicates a mixture that is rich or lean,
the oxygen sensor input to the ECM takes priority
over the control valve. The second oxygen sensor’s
output is used by the ECM to verify the catalyst is
operating properly by measuring how effectively it’s
storing and releasing oxygen.
The ECM will use the oxygen sensor information
to adjust the fuel control valve and throttle plate
actuator positions and provide the proper fuel
delivery. This compensation deviation commanded
by the ECM can be monitored using INSITE™. If the
compensation deviation exceeds set limits, the system
reverts to open loop operation.
Mass Air Flow System
Mass Air Flow (MAF) systems uses these parameters
as a basic method to calculate and determine fuel
delivery calculations and engine timing:
▪▪RPM
▪▪Mass (Volume) Air Flow
▪▪Air Temperature
▪▪Calculated Volumetric Efficiency
▪▪Base ignition timing = IMP X EPS
▪▪Engine Parameters
▪▪EP x VE x MAF/ AT = Formula to calculate
fuel delivery
ISX12G Cold Side

10ISX12-G Fuel Systems
Module One
Speed Density System (MAPT)
The Cummins ISX12G (Speed Density System) uses:
▪▪A Hall-effect Engine Speed Sensor to input
crankshaft speed (RPM)
▪▪A “smart” turbo air inlet temperature, pressure
and humidity sensor to determine oxygen content
of the incoming air
▪▪An Intake Manifold Pressure/Temperature sensor
to input the manifold charged air pressure and
charged air temperature entering the cylinders
▪▪A Mixer inlet pressure to monitor boost pressure
▪▪An exhaust gas oxygen sensor provides closed-
loop feedback for the ECM
▪▪An Engine Coolant Temperature sensor to input
coolant temperature
▪▪All combine to calculate the basic fuel requirement
at various engine operating conditions.
Fuel delivery calculations and ignition timing are
based upon:
▪▪RPM
▪▪Intake Manifold Pressure & Temp
▪▪Can be positive or negative pressure
▪▪Throttle Inlet Pressure/Temp/Humidity
▪▪Base ignition timing = IMP X EPS
▪▪Engine Parameters
▪▪RPM(EPS) x IMP/T x Engine Temp
▪▪To calculate fuel delivery
Engine Component Overview
(cold slide)
This is the “cold” side view of the engine with most
of the components visible and labeled. The cold
side is the intake side of the engine. The sensors are
colored green and the actuators are in black.
Engine Component Overview
(top side)
This is a top view of the engine with the top-side
components identified. Jacobs engine compression
braking is mentioned here but is not discussed as it is
not part of the fuel control system.
Cold Side
Top Side

11ISX12-G Fuel Systems
Engine Orientation
Engine Component Overview
(hot side of engine)
Here is the “hot” side of the engine showing the
component’s locations. The hot side is the exhaust
side of the engine. Notice that the location of
the coolant Temperature Sensor is on top of the
cylinder head/rocker box housing. The turbo turbine
Temperature Sensor is not truly visible at this
angle. Again, sensors in green, actuators in black,
and mechanical components in grey. We will be
reviewing these components in the systems that they
help to monitor and control.
Hot Side

12ISX12-G Fuel Systems
Activity 1.1:
ISX 12L Component Orientation
Locate these components on the engine and place the number or letter of the item in the space provided.
TEMPERATURE SENSORS:
1. Engine Coolant Temperature Sensor _______
2. Intake Manifold Pressure/Air Temperature Sensor _______
3. EGR Temperature Sensor _______
4. After-Treatment Catalyst Temperature Sensor _______
5. Turbocharger Turbine Inlet Temperature Sensor _______
6. Turbocharger Compressor Intake Air/Temp Sensor _______
7. Fuel Outlet Pressure/Temp. Sensor _______
8. Oil Temp Sensor _______
9. Turbine Temp Sensor _______
PRESSURE SENSORS:
10. Fuel Inlet Pressure Sensor _______
11. Intake Manifold Pressure / Temperature Sensor _______
12. EGR Delta Pressure Sensor _______
13. Mixer Intake Pressure Sensor (Boost Sensor) _______
14. Fuel Regulator Output Pressure / Temperature Sensor _______
15. Oil Pressure Sensor _______
16. Compressor Intake Temperature Humidity & Pressure Sensor _______
17. Crankcase Pressure Sensor _______
SIGNAL PRODUCING SENSORS:
18. Catalyst Inlet Heated Oxygen Sensor _______
19. Catalyst Outlet Heated Oxygen Sensor _______
20. Knock Sensors (front 1,2,3 – rear 4,5,6) ___--___
Module One

13ISX12-G Fuel Systems
POSITION SENSORS:
21. Throttle Plate Position Sensor _______
22. Accelerator Pedal Position Sensor’s (APP1 & APP2) _______
23. EGR Position Sensors 1, 2, 3 _______
24. Camshaft Speed/Position (timing) _______
25. Crankshaft Speed/Position (Speed) _______
MASS SENSING:
26. Mass Gas Flow Sensor _______
27. Mass Air Flow Sensor _______
OUTPUTS & ACTUATORS:
28. Fuel Control Valve _______
29. Wastegate Control Valve _______
30. Throttle Plate Actuator _______
31. Fuel Shutoff Valve _______
32. Ignition Control Module (ICM) Timing _______
33. Ignition Control Module (ICM) Reference _______
34. EGR Valve _______
35. Data Link (Communication) _______
OTHER SENSORS:
36. Coolant Level Sensor _______
37. Turbocharger Compressor Intake Humidity/Temp. Sensor _______
OTHER DEVICES:
38. ECM _______
Engine Orientation

14 ISX12-G Fuel Systems
Module Two
2

15ISX12-G Fuel Systems
Chassis Fuel Flow CNG/LNG
Fuel Flow Overview
The system’s approach shows the path that the
natural gas travels starting on the chassis side through
various components and on to the engine ending up
at the engine intake. This approach will begin with
the fuel in the storage medium and follow it through
to the cylinder.
Note that overview shows two systems, one storing
the fuel as a gas (CNG Storage) and the other storing
the gas as a liquid. The engine runs on Natural Gas
(NG) that is converted from the storage medium.
There are advantages and disadvantages for each type
of storage. By storing CNG (Compressed Natural
Gas), the gas can stay in a specially designed storage
container for an indefinite length of time, until
the gas is used up. Liquefied Natural Gas (LNG),
cryogenic liquid, is stored in a thermos bottle-type
container because the temperature is -240 °F. Because
the contents in this storage container will warm up
over time, the liquid will turn back into a vapor,
which will in turn be vented off to the atmosphere.
LNG vehicles cannot be parked inside for this
reason. LNG containers have a check valve that
allows the container to vent excess pressure above
240psi. Because of this, LNG containers will empty
if the fuel is not used in a period of 2 – 3 weeks. The
primary advantage of using LNG storage is that by
chilling LNG into a liquid, reduces it to 600:1 or
1/600
th
the volume, which increases the time between
refills. LNG, like CNG, is made up of more than 90%
methane; in addition, LNG is even a more pure form
of NG.
CNG Fuel Flow
We begin with CNG as it is most common. CNG is
stored in a container at very high pressure between
3000-3600 psi. These containers have a special safety
device called a Pressure Relief Device (PRD) that
will protect the container from excessive pressure
or excessive temperatures. If the manufacturer
designated temperature or pressure is exceeded, the
PRD will release. The gas flows from the storage
cylinder to a high pressure normally-closed (N/C)
Shut-off Solenoid that is supplied by the Original
Equipment Manufacturer (OEM). The purpose of this
valve is to shut off the fuel when the engine is not
running. This valve is connected to the vehicle ECM,
which will turn off the valve if engine RPM is not
present (usually < 200 RPM). This valve is required
in California by law by CHP Title 13. Just beyond
the shut-off valve is the High Pressure Regulator.
This is designed to lower the system pressure to
approximately 100-125 psi. The two brass hose
fittings at the lower portion of the regulator are used
to flow coolant through a separate jacket to keep the
regulator from icing and sticking. This condition
is an issue due to the extreme drop in fuel pressure
because as gas flows, it rapidly expands and cools.
This phenomenon, the Joule Thomson expansion
effect, can cause dramatic gas temperature drops.
Although the regulator may be heated, the cold gas
exiting the regulator at pressure can deposit ice in the
outlet port, which will reduce the port size, causing
pressure control problems. This can result in poor
vehicle drivability, poor acceleration, and increased
engine exhaust emissions.
The coolant passing through the regulator also
keeps gas seals from becoming excessively cold
and leaking.

16ISX12-G Fuel Systems
Module Two
There are a couple of variations to the fuel flow. The
N/C shut-off solenoid can be mounted at the end of
the storage cylinder making it part of the cylinder
itself. Another variation is that the order of the high-
pressure shut-off valve order can be reversed so that
fuel flows through the secondary regulator before the
shut-off valve.
LNG Fuel Flow
Some applications may utilize LNG as the fuel
storage medium. The systems are identical after the
fuel reaches the shut-off valve. The temperature of
the fuel might be considerably lower than with CNG,
which will be addressed with the Mass Gas Sensor
and fuel temperature sensor at the secondary fuel
pressure regulator. The difference isn’t that large as
there is a refrigeration effect for CNG as the pressure
drops through the first-stage regulator.
In a system that stores NG as a liquid fuel, when the
fuel exits the LNG storage container, it immediately
is routed through a vaporizer. This is usually mounted
at the end or just next to the storage container. The
purpose of the vaporizer is to warm the liquid and
transform it back into a gas. The vaporizer has warm
coolant lines running though it that warm the fuel,
converting it back into the a gas.
After the fuel exits the vaporizer, the same variations
exist for the shut-off valve and the fuel regulator as
the order of the high-pressure shut-off valve order can
be reversed so that fuel flows through the secondary
regulator before the shut-off valve.
CNG Storage
The OEM chassis supplier determines the
manufacturer, placement and other factors concerning
the storage cylinder.
Cylinder types can be type 1, 2, 3 or 4 and in
multiple tank arrays. Today, most cylinders have
N/C electronic shut-off valves on the tank, which are
controlled by the ignition switch or the ECM.
CNG Cylinders LNG Logo
Roof Mounted CNG Cylinders

17ISX12-G Fuel Systems
Chassis Fuel Flow CNG/LNG
LNG Storage
There are several suppliers of LNG on-road storage
cylinders. The OEM determines which manufacturer and
the placement of the storage cylinder on the vehicle.
▪Low Pressure Storage Vessels have a stainless-
steel outer shell and also have insulated stainless
steel inner tank
▪Multiple tanks are often optional on vehicles
▪Container regulated pressure is 230 psi maximum
▪Fuel stored at < -230 psi with a check valve will
release if pressure exceeds this limit
CNG/LNG Common Components
The OEM determines the manufacturer/supplier of all
components prior to the Cummins dual parallel fuel
fi lters. Once the fuel has been reduced to low pressure
NG, it is introduced to the fi lters.
▪The N/C High-Pressure Shut-Off Solenoid is
OEM supplied
▪Controlled by Ignition Switch or by ECM to
prevent fuel fl ow from storage vessel with
ignition OFF
OEM supplied (Primary) High Pressure regulator.
High pressure regulators may have coolant lines
attached to them to avoid regulator icing, which
occurs with the pressure drop.
On LNG systems, the combination Pressure Building/
Economizer Regulator is a two-in-one, or dual
function, regulator. The single regulator maintains
a minimum pressure in the tank by regulating the
pressure-building function and relieves excess
pressure when the tank pressure is high, effectively
lowering the pressure in the tank to the economizer
regulator set point. Combination regulators are
generally designed so that there is a “sweet zone” or
pressure zone when neither the pressure-building nor
the economizer functions are operating (although not
in all cases).
LNG Tank
Fuel Shut-off Solenoid
ITT Regulator Economizer Regulator

18ISX12-G Fuel Systems
Module Two
Natural Gas Fuel Flow
These Cummins supplied 25-micron contaminant and
0.3-micron oil vapor coalescing fuel filters double the
surface area of filtration and provide drains to release
moisture and oil contaminants. Cummins has doubled
the filtering capacity and increased the passage
volume to allow for the additional fuel required
for this larger platform by plumbing two filters in
parallel.
Natural Gas Fuel Filters
In CNG systems, there are issues where CNG
compressor oil can pass through the station
compressor and enter the vehicle through the filling
station. If the compressor oil comes in contact with
the Mass Gas Sensor, erroneous readings can occur
by the sensor by insulating the hot wire of the sensor.
Because of this, it is important to keep the coalescent
filters maintained on CNG vehicles to prevent oil
contamination of the various sensors that it may
come in contact with. Coalescing Filters remove solid
contaminants to 25 microns and oil vapors to 0.3
microns (3/10,000,000 of a meter!)
Dual Filters with Drains
After the NG flows through the coalescing filters,
it arrives at the low pressure fuel regulator housing
where fuel pressure is dropped again by the low-
pressure fuel regulator (secondary regulator) and the
pressure is acceptable for delivery to the engine Fuel
Control Valve.

19ISX12-G Fuel Systems
Chassis Fuel Flow CNG/LNG

20 ISX12-G Fuel Systems
Module Three
3

21ISX12-G Fuel Systems
Engine Fuel Flow System
Low Pressure Fuel Regulator
Assembly
The secondary or low-pressure fuel regulator housing
is located on the “cold” side of the engine near the
rear and contains the following items:
The regulator itself with preset internal spring and
spool valve, N/C Fuel shut-off solenoid, that is
connected to the ECM shuts off when engine RPM is
not present.
Primary fuel pressure sensor reports fuel pressure
for fuel coming into the engine low-pressure fuel
regulator assembly wastegate control valve to
control Turbo waste gate. Pressure tap ports; Inlet
fitting from fuel filters; Fuel pressure boost assist
diaphragm; Boost signal line fittings
Low (Secondary) Pressure
Regulator
Cummins color codes the regulator (spool valve) for
the ISX12G and ISL-G engines. The ISL-G 8.9 L is
black and the ISX 12L is red. The size of the ports are
considerably smaller on the ISL-G.
Low Pressure Regulator Assembly
This regulator reduces the fuel pressure to approximately 60 psi. Notice the vacuum line to
increase outlet pressure based upon amount of boost.
Low-Pressure Shut-off Valve
As dictated by California law (CHP title 13), all
combustible engines must have a means to stop fuel
flow to the engine in the event the engine dies or the
fuel lines become damaged. NG engines use two shut-
off valves to automatically close in the event the engine
rpm signal is lost or the ignition switch is turned off.
This is controlled by the ECM, which shuts off the
valve if engine rpm is not present or < 100 rpm.
This valve is normally closed 12v valve in the low-
pressure stream that opens when energized to allow
fuel flow.
To test the valve, back probe the connector at pin
C while cranking and you should see 12 volts. The
resistance with the connector disconnected should be
3 to 5 Ohms. Resistance should be checked when the
valve is both hot and cold and should not vary more
than 10%.
Secondary Regulator Spool Valve
Low Pressure Shut-off Solenoid

22ISX12-G Fuel Systems
Fuel (Inlet) Pressure Sensor
The Inlet Pressure Sensor is a typical three-wire 5-volt
pressure transducer sensor. Its purpose is to protect
the fuel housing components of the fuel system in the
event high pressure regulator malfunctions, causing
excessive fuel pressure to the low pressure regulator.
If this occurs, a fault code will be set and an amber
warning light will also occur. This will happen when
high or low fuel-pressure limits are exceeded.
To test this pressure sensor, measure voltage at pin B
with a DVOM and note changes when fuel pressure
varies. Optionally, you can connect a mechanical
gauge or an external pressure transducer for a
DVOM to the pressure ports to monitor fuel pressure.
These ports are on the Low-Pressure Fuel Regulator
Assembly. Note that gauge pressure is about 15 psi
less than what you see on INSITE™ as INSITE™ is
showing actual pressure, which most gauges do not.
This gauge is reading the pressure above atmospheric,
which means the gauge starts at zero not the 14.7 psi
present in the atmosphere.
Fuel Inlet Pressure Sensor
Wastegate Control Valve
The default closed position of the waste control valve allows full boost pressure to act on the
wastegate in the event there is a malfunction of
the valve or the various sensors that monitor boost
pressure. In normal operation, the valve bleeds
off pressure applied to the wastegate to allow for
increases in turbo boost pressure as load or power
requirements dictate.
This valve is a two-wire solenoid and will limit
boost to 5 psi if the valve malfunctions. Checks
for continuity and valve movement can be
accomplished. This valve can only be operationally
tested while under load.
This valve is what we call “high-side” controlled as
the ECM powers up the valve to actuate it instead
of grounding it. This is done for a safety factor to
prevent accidental grounding of the solenoid valve
and unwanted actuation.
To test this valve, use an ohmmeter to test the
solenoid coil. In addition, the signal to this valve is
PWM so the duty can be tested for this valve. Higher
duty cycle will equal more boost.
Fuel Inlet Pressure Sensor
Wastegate Control Valve
Module Three

23ISX12-G Fuel Systems
Natural Gas Fuel Flow
The fuel delivery hose is supplied by Cummins and is
not repairable; it should be replaced with the proper
Cummins supplied part. This hose comes from the
vehicle chassis coalescing filters and goes to the low
pressure regulator housing
Fuel Control Module
The fuel flows to the Fuel Control Module and
intake manifold through the fuel transfer tube and
a laminar flow screen. It is mounted to the bottom
of the intake manifold where the fuel enters. The
various fuel characteristics are measured here and
fuel is then allowed to flow into the intake manifold
mixer assembly via the fuel control valve. The fuel
control valve is basically one large fuel injector so it
is similar to a gasoline throttle body injection system
but flows fuel below the throttle blade instead of
before it as in a gasoline engine. The fuel control
valve is pulse-width modulated or duty-cycle, which
is a percentage of time open versus time closed. A
25% duty cycle means open 25% of the time and
closed 75% of the time. As fuel demand increases the
amount of Fuel Control Valve time open increases
and the time closed decreases.
Valve is “High Side” Controlled
The fuel flow venturi speeds up the fuel flow to the outlet of the housing and allows 10% of the gases to
flow past the gas mass sensor where the 10% of total
gas flow is measured and then the remaining amount
is calculated before it reaches the fuel control valve.
Fuel Control Housing
The fuel pressure is shown in absolute pressure as
presented in INSITE™™, and not gauge pressure.
The laminar flow screen can be installed backwards
and proper orientation is necessary for proper fuel
flow into the venturi. Its purpose is to smooth out the
flow of fuel as it enters the venturi.
Fuel Control Housing
Engine Fuel Flow System

24ISX12-G Fuel Systems
Fuel Control Venturi
The ports on the side of the venturi is where 10% of
the fuel is received as it returns from the gas mass
sensor. The majority of the fuel is accelerated through
the center, where it encounters the fuel control valve.
The fuel flows around the outside of the venturi
horn inlet to the gas mass sensor ports, where it is
measured for volume and density.
Mass Gas Flow Sensor
This sensor, mounted in the fuel housing, operates
basically the same as all hot-wire type flow sensors. It
is used to sense the flow of gas into the control valve.
A heated element is cooled by the flow of the
gas, and the ECM ramps up current to maintain a
predetermined temperature of the sensing wire. A
Negative Temperature Coefficient (NTC) thermistor
measures the temperature of the sensing wire and
signals to the ECM what the temperature is. The
amount of current (displayed in voltage) determines
the volume or mass of fuel that is flowing and
becomes part of the fuel trim formula.
Fuel Control Venturi
The signal from the Mass Gas Sensor represents low
voltage = low flow and high voltage = high flow as
these values are monitored in INSITE™. A major
concern with this sensor is that oil contamination
that can come in with the fuel can coat this sensor
and give false readings. This would result in poor
performance and efficiency.
A DVOM can be used to monitor the voltage change
at the signal wire and return. INSITE™ can also be
used to monitor the sensor activity.
NOTE: This sensor requires a 15-volt supply
to operate properly. There is a voltage
amplifier circuit in the ECM that steps up
the voltage to this sensor. This is the only
sensor requiring 15v.
Mass Gas Flow Sensor
Module Three

25ISX12-G Fuel Systems
Fuel Control Valve
The Fuel Control valve is a normally closed valve,
similar to other engine models, with inlet and outlet
ports calibrated for the engine flow rate. They are
different sizes with double O-ring seals to prevent
fuel leakage. This valve is pulse-width modulated
solenoid, as are conventional injectors.
INSITE™ provides a duty-cycle parameter for
this solenoid. When checking this valve, check for
resistance (3-5 Ohms) both hot and cold with no
more than 10% change. Also check for sticking.
The digital lab scope is the preferred method to view
the pulse-width signal as INSITE™ will only provide
the duty-cycle as a parameter.
This is a two wire N/C valve. This is like one large
injector that delivers fuel to the mixer instead of one
for each cylinder. The resistance of this valve is 3 to
5 ohms. When checking this valve, check resistance
both hot and cold and confirm that the resistance is
not more than 10%. This valve is known to stick,
or the coil can open. Remember that the ECM
commands this valve and does not confirm that the
valve is functioning properly other than by getting
feedback through the Mass Gas Sensor.
Fuel Control Valve
Natural Gas Fuel Flow
After the fuel is released by the fuel control valve, it enters the intake manifold where it becomes mixed
with charged air and is distributed to each cylinder.
Inlet Temperature/Pressure/Humidity
Engine Fuel Flow System

Module Four
4
26 ISX12-G Fuel Systems

27ISX12-G Fuel Systems
Engine Air Flow System
Air Flow Overview
This is an overview of the air flow as it enters the
engine starting with the air filter supplied by the OEM.
The air is drawn in through the OEM-installed air
filter where it enters the Turbocharger Compressor
Inlet housing. The air filter is typically a paper-type
pleated filter.
The Turbocharger Compressor Inlet housing
connects the Air Cleaner to the turbocharger. This
housing also contains the Inlet Air Temperature,
Pressure & Humidity sensor. This sensor provides
air temperature, pressure and humidity to the ECM,
which uses the information to fuel trim and the
proper ignition timing.
The compressor Inlet Temperature, Pressure &
Humidity Sensor is a “smart” Sensor. This means that
it contains a microprocessor that generates a CAN
signal. In this signal, the temperature, pressure &
humidity of ambient air is broadcast over the CAN
bus to the ECM, which is then interpreted. These
values are used in fuel trim and timing calculations.
Compressor Inlet Temperature,
Pressure & Humidity Sensor
The Compressor Inlet, Temperature, Pressure &
humidity Sensor is a smart sensor that is connected to
the CAN network, it is necessary to use INSITE™ to
monitor the parameters of this sensor.
Turbocharger Compressor
The turbocharger compressor vane has fixed pitch
blades. The integral wastegate valve on the turbine
limits the boost to 25 psi.
Air Charge Cooler
The purpose of an intercooler is to cool air that has
been compressed in either a turbo or supercharger.
The temperature of compressed air rises
dramatically - upward of 300 °F and becomes less
dense and less oxygen rich. An intercooler is like a
heat exchanger. The ISX12G intercooler is designed
to reduce air temperature by 8 degrees.
There are two main types of intercoolers and: air-
to-air and air-to-water. An air-to-air intercooler uses
outside air to transfer heat, while an air-to-water
uses water to transfer heat. This is the air-to-air
charge intercooler.
Hot Side
Inlet Temperature, Pressure, Humidity Sensor

28ISX12-G Fuel Systems
Throttle Inlet Housing
The Throttle Inlet housing connects the Air Charge
cooler to the mixer housing which provides the
charged air to the mixer.
This Inlet housing also contains the Throttle Intake
Pressure (Boost) sensor and the Mass Air Flow Sensor.
The throttle Intake pressure inlet boost sensor provides
boost pressure information to the ECM.
The Mass Air Flow sensor has been eliminated on
some engines and the actual MAF value is calculated
in some calibrations.
Mixer Intake Pressure (Boost)
Sensor
The Throttle Intake Pressure (Boost) Sensor measures
boost pressure while under load and atmospheric
pressure when not under load. From this, the ECM
calculates air density and determines the engine’s air
mass flow rate, which in turn determines the required
fuel metering for optimum combustion and influences
the advance or retard of ignition timing.
The boost sensor is a three-wire sensor as in all
pressure transducers. It has a 5 volt reference, with
signal and return lines. When taking measurements
for pressure and comparing to known good values,
always use the signal and return connections. Also
confirm that the sensor has the appropriate 5 volts to
operate properly.
Throttle Actuator
The throttle actuator is located on the front side of the
intake manifold/mixer housing, It is used to control
engine speed through drive-by-wire throttle. The
ECM controls the throttle plate opening based upon
demand from the driver and need.
The ECM sends a pulse width modulated (PWM)
signal to the throttle plate actuator motor. The throttle
plate actuator opens or closes the throttle plate in
response to the PWM signal. This actuator also has
position sensors that report the throttle position
information back to the ECM.
This signal is based upon demand for load by APP1
and APP2, the two Accelerator Pedal Position Sensor
signals that are sent to the ECM based upon driver’s
foot request.
The Throttle Actuator six-wire plug has the 5 volt
reference, with a common return. The voltage is
pulsed to ATA- and ATA + as a command to open and
close the throttle. TPP1 And TPP2 are sensor signals
to the ECM that identify the position of the throttle
plate.
Boost Pressure Sensor 3 wire
Throttle Motor Assembly
Module Four

29ISX12-G Fuel Systems
Throttle Plate Position
Sensors 1 & 2
This engine runs a fly-by-wire throttle system. The
driver signals demand for acceleration to the ECM
and the ECM moves the throttle plate as needed.
Potentiometers are used to see where the throttle
plate is currently positioned.
The ECM uses the measured position (sensed
position) of the throttle plate potentiometer to control
fueling and engine speed. There are two sensors
(TPP1 and TPP2), and the ECM compares these two
signals to ensure they match as a means of safety and
redundancy. If they do not match or compare to the
command opening, then the system sets a fault and
goes into an idle-only mode.
These potentiometers are three-wire sensors that run
on a common 5 volt reference with a return. The
movable arm in the sensor returns a portion of the
voltage to the ECM with throttle plate movement.
When performing a normal voltage check on TPP1
and TPP2, you will observe that one sensor’s voltage
starts higher and goes up while the other sensor’s
voltage starts lower and goes higher.
Mixer Assembly
The mixer assembly is used to thoroughly mix
air, fuel and exhaust gases before they enter the
combustion chamber. It is located inside the Intake
manifold and has the EGR valve and fuel control
housing connected to it. Removing this mixer
housing requires a special tool from Cummins.
(Cummins P/N 2892416)
Mixer Venturi
Special Tool Used to Remove Mixer Venturi
Engine Air Flow System

30 ISX12-G Fuel Systems
Activity 1.2:
Fuel Control Valve & Mixer Assembly Inspection
Tools and equipment:
1. Cummins documentations 2. Hand Tool Set
Step 1: Turn off the fuel system to engine, start engine and run out of fuel to bleed lines in preparation
of removing the Fuel Control Valve and Mixer Assembly.
Step 2: Using the appropriate tools remove the Mixer Assembly.
Step 3: Using the appropriate tools remove the Fuel Control Valve.
Lab Activity 1.1
Fuel Control Valve & Mixer Assembly Inspection

1
Student Name __________________________ Date _____________________

Tools and equipment:
1. Cummins documentations 2. Hand Tool Set
Step 1: Turn off the fuel system to engine, start engine and run out of fuel to bleed lines in preparation of
removing the Fuel Control Valve and Mixer Assembly.
Step 2: Using the appropriate tools remove the Mixer Assembly
Step 3: Using the appropriate tools remove the Fuel Control Valve

Module Four

31ISX12-G Fuel Systems
Step 4: Identify the following components and state their function below.
a) Low (secondary) Regulator Outlet Pressure /Temperature Sensor
Function: ___________________________________
b) Low Pressure Regulator
Function: ___________________________________
c) EGR Differential Pressure Sensor
Function: ___________________________________
d) Intake Manifold Pressure/Temperature Sensor
Function: ___________________________________
e) Throttle Intake (Boost) Pressure Sensor
Function: ___________________________________
f) Throttle Actuator
Function: ___________________________________
g) Fuel Regulator (primary) Intake Pressure Sensor
Function: ___________________________________
h) Boost Pressure Air Line
Function: ___________________________________
i) Wastegate Control Valve
Function: ___________________________________
j) Fuel Shutoff Valve
Function: ___________________________________
k) Fuel Transfer Tube
Function: ___________________________________
l) Gas Mass Flow Sensor
Function: ___________________________________
m) Fuel Control Valve
Function: ___________________________________
n) Mass Air Flow Sensor
Function: ___________________________________
o) OEM fuel Supply
Pressure: ______________When?_______________
What components does Cummins require the OEM to provide?
1.___________________________________
2.___________________________________
3.___________________________________
p) EGR Motors and Position Sensors
Function: ___________________________________
q) EGR Temperature Sensor
Function: ___________________________________
Step 5: Resemble Mixer Assembly and Fuel Control Valve Assembly.
Step 6: Reinstall in ISX 12G engine.
Step 7: Start engine and confirm proper operation.
Engine Air Flow System

32ISX12-G Fuel Systems
Intake Manifold Pressure/
Temperature Sensor
The Intake Manifold Pressure Sensor/Temperature
Sensor, a combination sensor, is located at the
rear of the Intake Manifold. Its job is to sense
the charge air temperature and pressure in the
manifold, which is used to determine engine
timing and boost requirements.
The ECM uses the intake manifold pressure
information to control engine fueling and boost. The
intake manifold temperature information is used for
engine overheat protection due to hot intake air.
The combination Intake Manifold Pressure/
Temperature Sensor contains a four-wire plug that
which has the 5 volt reference, a pressure signal
input and temperature signal output and returns.
There are separate circuits for the pressure signal
and temperature signal. The temperature signal is
a thermistor that should be measured between the
temperature signal and the common signal return.
The pressure signal is a transducer that should be
measured between the pressure signal and ground.
Verifying the readings with known good values will
determine if the components are accurate.
Temperature Sensors
A thermistor is an electrical device that changes
resistance as the temperature changes. There are two
types of thermistor devices, Negative Temperature
Coefficient (NTC) and Positive Temperature
Coefficient (PTC). The NTC thermistor is the most
accurate and is commonly used in the automotive
world. The resistance change across this device is
linear. In a NTC thermistor, resistance is high when
cold and low when hot. The PTC thermistor reacts in
the opposite direction. It is low when cold and high
when hot.
In order to have a voltage change in this temperature
circuit, we need to add a fixed resistor in series
with the thermistor. This resistor is actually inside
the ECM so the two resistors are in series making a
voltage divider circuit with each resistor acting as a
load. According to Kirchoff’s law, the sum of all loads
will equal the source voltage. When the resistance
changes across the thermistor device (due to
temperature) the voltage dropped across each resistor
changes. The voltage drop across the thermistor (5V
signal and Signal Return) is what the ECM looks at to
correspond to the actual temperature.
Manifold Pressure Temperature Connector
Checking Voltage with a DVOM
Module Four

33ISX12-G Fuel Systems
Kirchoff’s law
1. 100% of supplied voltage is consumed by circuit.
2. The Voltage Drop across the fixed resistor will be
proportional to the resistance value of the thermistor
and its Voltage Drop.
An Open circuit would allow NO current flow…no
voltage drop and the voltage at the signal would be 5V.
Vd=It x R(x)
A shorted circuit on the supply side of the thermistor
would be 0 volts at the signal as all the voltage would
be consumed by the fixed resistor.
Measuring Voltage
There are two ways to test thermistor devices:
measuring resistance and measuring voltage.
When measuring voltage, the thermistor device is left
connected in the circuit and the circuit is powered up.
The voltage drop is measured across the 5V signal
and signal return pins by back probing the thermistor
connector. We then can compare this voltage drop
with known good values for the actual temperature of
the sensor.
Testing Temperature Sensors
(measuring resistance)
Another way to test thermistors is to measure the
resistance of the device. To do this it will need to be
disconnected from the circuit for two reasons:
1. The meter will provide its own power.
2. We only want to measure the resistance of the
thermistor device. After being disconnected, you
would measure the resistance at the signal and return
pins on the thermistor device.
Pressure Sensors
When working with pressure sensors, we need to take
into consideration what pressure is being measured.
Atmospheric Pressure is the pressure around us and
is referred to as barometric pressure. It is affected by
altitude and weather conditions. The readings at sea
level are reduced by 1”Hg (inches of mercury) for
every 1000 feet of altitude.
Sea level = 29.8“Hg or 14.64 psi
4.5 psi = 100 kPa = 1 BAR @ 32 °F
Absolute Pressure is the pressure without
atmospheric pressure’s influence. These gauges
would read 14.7 psi lower at sea level.
Testing Pressure Sensors
Pressure Sensors are typically transducer devices and
require power to operate, therefore there is a third
wire to power the device. The other two wires are
the pressure signal and the signal return. To measure
a pressure sensor, you need to measure (back probe)
across the pressure signal and return with a volt
meter. This is always performed with the circuit
energized. You would then monitor the voltage as the
pressure changes and compare to known good values.
Engine Air Flow System

34 ISX12-G Fuel Systems
Catalyst Temperature Sensor
Tools and equipment:
1. Cummins Troubleshooting and Repair Manual 2. INSITE™
3. Infrared Pyrometer 4. DVOM
Step 1 Using the repair manual locate the CAT TEMP wiring diagram
Catalyst – 5-volt reference wire terminal _________
Sensor return wire terminal _________
Step 2
Back probe the sensor’s signal wire.
Connect INSITE™ and view temperature parameters.
Aim the infrared pyrometer at the sensor and compare the temp and resistance to the specs
Temp ______________ Resistance ______________ Is it within range? Yes / No
With KOEO record the temperature and DVOM resistance below.
With KOEO record the temperature with the infrared pyrometer below.
With KOEO record the voltage and DVOM voltage below.
With KOEO record the voltage and temperature from INSITE™.
With KOER log temperature and voltage readings at 30-second intervals and record in the spaces provided
below. At the end, re-measure DVOM resistance.
� KOEO 30 60 90 120 150 180 210
Step 3 Using INSITE™ record diagnostic codes and temperature readings.
Diagnostic Trouble Codes (DTC) ______________Temperature reading _____________________
Step 4 Short the harness connector and record the temperature and diagnostic code from INSITE™
Diagnostic Trouble Code __________________ Temperature reading _____________________
Activity 1.3:
Testing & Versifying Temperature & Pressure Sensors
Pyrometer
DVOM
INSITE™/
TEMP/V
Module Four

35ISX12-G Fuel Systems
Engine Coolant Temperature Sensor
Tools and equipment:
1. Cummins Troubleshooting and Repair Manual 2. INSITE™
3. Infrared Pyrometer 4. DVOM
Step 1 Using the repair manual locate the ECM wiring diagram
ECT – 5-volt reference wire terminal _________
Sensor return wire terminal _________
Step 2
Back probe the sensor’s signal wire.
Connect INSITE™ and view temperature parameters.
Aim the infrared pyrometer at the sensor and compare the temp and resistance to the specs
Temp ______________ Resistance ______________ Is it within range? Yes / No
With KOEO record the temperature and DVOM resistance below.
With KOEO record the temperature with the infrared pyrometer below.
With KOEO record the voltage and DVOM voltage below.
With KOEO record the voltage and temperature from INSITE™.
With KOER log temperature and voltage readings at 30-second intervals and record in the spaces
provided below. At the end, re-measure DVOM resistance.
� KOEO 30 60 90 120 150 180 210 �
Step 3 Using INSITE™ record diagnostic codes and temperature readings.
Diagnostic Trouble Codes (DTC) _______________ Temperature reading ____________________
Step 4 Short the harness connector and record the temperature and diagnostic code from INSITE™
Diagnostic Trouble Code __________________ Temperature reading _____________________
Pyrometer
DVOM
INSITE™/
TEMP/V
Engine Air Flow System

36 ISX12-G Fuel Systems
Module Five
5

37ISX12-G Fuel Systems
Exhaust Gas System
ECM uses the Turbine ITS
Excessive exhaust heat is caused by excess fuel
and turbo boost. Excessive heat in the exhaust will
cause a failure of the catalytic converter as the
substrate will melt down and blockage will occur.
Excessive temperatures may initiate a power de-
rating by the ECM.
Turbine Inlet Temperature Sensor
Testing
The pyrometer-type temperature sensor has two
wires, signal and return, and works much like a
thermistor. To test this sensor, you would measure the
resistance across the signal and return and compare
the resistance with known good values for the given
temperature of this sensor.
Catalyst Inlet Oxygen Sensor
The Catalyst Inlet Oxygen Sensor is mounted in the
turbocharger adapter housing, which is the path the
exhaust uses to exit the turbo and go to the catalytic
converter. The catalyst oxygen sensor determines
the amount of oxygen in the exhaust gas. The
amount of oxygen in the exhaust gas indicates the
actual air:fuel ratio information that is used by the
Pyrometer
Exhaust Gas Flow Overview
This is an overview of the Exhaust Gas flow as it exits the engine on the Cummins ISX 12L platform.
The exhaust exits the exhaust ports, travels to the
turbocharger turbine and then to the exhaust after-
treatment catalyst before it exits the vehicle chassis.
Turbine Inlet Temperature Sensor
The turbine inlet temperature sensor is in the path
where the exhaust enters the turbine. This senses
the temperature of the exhaust stream. A bi-metallic
pyrometer-type sensor is utilized as it can handle
much higher temperatures than a thermistor. It is
used for critical protection preventing turbo and
catalyst overheating.
Turbine Inlet Temperature Sensor
Connector

38ISX12-G Fuel Systems
ECM to calculate the proper amount of fuel required
during closed-loop operation.
The inlet oxygen sensor’s output is used by the ECM
to verify that the fuel control valve position and
the throttle plate actuator position are providing the
desired exhaust gas condition. The ECM can increase
or decrease the amount of oxygen in the exhaust by
adjusting the air-to-fuel ratio. This control scheme
allows the ECM to make sure that the engine is
running at close to the ideal or stoiciometric point,
and also to make sure that there is enough oxygen
in the exhaust to allow the oxidization catalyst to
oxidize the unburned hydrocarbons and CO.
The catalyst inlet oxygen sensor consists of two
platinum electrodes separated by a Zirconia (Z
r
O
2
)
element. The outer platinum electrode is exposed
to the exhaust gas. The inner platinum electrode is
vented to the atmosphere, in some cases through the
lead wires. When heated to above approximately
700 °F (370 °C) by the heater element and exhaust
temperature, the zirconia element in the oxygen
sensor becomes conductive. The two platinum
electrodes then act as the plates of a battery, with the
zirconia acting as the electrolyte of the battery. The
galvanic reaction creates a voltage output between .1
and .9v.
This sensor can be coated and have false readings
when EGR cooler leaks into system.
Testing Heated Oxygen Sensors
The voltage output of the sensor is read using
an electronic service tool such as INSITE™ or
manually tested using a voltmeter or Digital Storage
Oscilloscope (DSO).
The sensor should be capable of reaching both .1 and
.9v thresholds when driven lean and rich. Propane
enrichment is used to drive the system lean. The time
it takes to return to a rich condition is called the Rise
Time of the sensor.
You must use a DSO to measure rise time as you
CANNOT see rise time or measure it accurately with
a DVOM. The sensor should drive from lean to rich
in under 100ms when the test is performed or the
sensor is lazy.
CAUTION: Forcing the system rich can cause
damage to the catalyst if done excessively.
Catalyst Inlet O
2
Sensor and Heater
Testing O
2
Thresholds
Module Five

39ISX12-G Fuel Systems
Catalyst Temperature Sensor
The location of this sensor is at the output of the
catalytic converter.
The catalyst temperature is also a bi-metallic
pyrometer type temperature sensor. It is a two-wire
sensor that works much like the thermistors but at
higher temperatures. Using known good resistances
for given temperatures can be helpful to check
calibration.
This sensor monitors the temperature of the exhaust
gas after the two catalysts. If the exhaust gas
temperature exceeds the specified setting of 1350 °F
(732 °C) the ECM will severely de-rate the engine
to keep the high temperature exhaust gas from
damaging the catalyst bricks. At 1375 °F (746 °C)
engine shutdown will occur.
Catalyst Temperature
Sensor
Pyrometer
Catalyst Outlet Oxygen Sensor
The Catalytic Outlet Oxygen sensor is mounted at the
outlet of the catalytic converter. It senses the exiting
exhaust to confirm proper catalytic converter operation.
The sensor functions in the same manner as the
catalyst inlet oxygen sensor, but is used to verify cat
operation and is not used to determine the proper
air:fuel ratio.
The output of this sensor is used by the ECM for
verification of proper operation of the three-way
catalyst. When operating efficiently, the rear portion
of the catalytic converter absorbs oxygen to continue
the burning of the HC and CO. The voltage is
normally flat-lined if the O
2
is being absorbed.
The voltage output of the sensor is tested much the
same as the inlet sensor. Because it is usually flatlined
in a rich condition (.7-.9v) it won’t fluctuate except
during warmup. It can be forced rich and lean similar
to the inlet sensor.
CAUTION: Forcing the system rich can cause
damage to the catalyst if done excessively.
Catalyst Outlet O
2
Exhaust Gas System

40ISX12-G Fuel Systems
Catalyst Inlet & Outlet Oxygen Sensors
Tools and equipment:
1. Cummins Troubleshooting and Repair Manual 2. (2) DVOM’s
3. Infrared Pyrometer 4. Propane Enrichment Tool

Step 1: Using the Classroom manual, locate the Catalyst Inlet & Outlet Oxygen Sensor wiring diagram:
Inlet Outlet
HOS signal Wire terminal ___________ ____________
HOS signal return Wire terminal ___________ ____________
12v heater supply Wire terminal ___________ ____________
12v heater return Wire terminal ___________ ____________
Step 2: Do the wire terminals of the wiring diagram and the harness coincide? YES or NO
Step 3:
Back probe Inlet O
2
sensor Signal & Return to the 2 DVOM’s
Set one DVOM to measure milli-volts and the other to measure frequency, while using the Min/Max function
on the DVOM
Start engine, and confirm proper DVOM operation (KOER)
What is the temperature of the Catalytic Converter on the Inlet side? ____________
What is the temperature of the Catalytic Converter on the Outlet side? ____________
Step 4:
Insert a propane enrichment tool into the intake system.
Open the propane valve to create a rich mixture over 800mv
Close the valve and create a lean mixture under 175mv
Snap the throttle and measure the rise time under 100ms
What is the temperature of the Catalytic Converter on the Inlet side? ____________
What is the temperature of the Catalytic Converter on the Outlet side? ____________
Was there a temperature change by doing the Propane enrichment? _______________
Why or Why not? _____________________________________________________
Activity 1.4:
Testing & Versifying Signal Producing Sensors
Module Five

41ISX12-G Fuel Systems
Exhaust Gas System
Step 5: Repeat step 1-4 with the Catalyst Outlet Oxygen Sensor
Was there any difference in the results/readings for the Catalyst Outlet Sensor? _________________
Why or why not? ___________________________________________________________
Step 6:
Note the readings of the FUEL CONTROL VALVE while performing the propane enrichment exercise
and write the value in the space provided __________________________
Note the readings of the FUEL CONTROL VALVE while performing the FULL STALL TEST without
propane enrichment and write the value in the space provided ________________________
Note the readings of the FUEL CONTROL VALVE @ idle and write the value in the space provided
____________________________________

42ISX12-G Fuel Systems
Exhaust Gas Flow Overview
Some of the exhaust also exits the cylinder head and
travels to the EGR cooler and the EGR transfer tube.
We are now going to discuss this path.
EGR Cooler
The ISX12-G - G engine is equipped with a cooled
EGR system. The EGR cooler is mounted on the right
side of the engine just above the exhaust manifold.
The EGR control valve is mounted on the cold side,
high on the engine, on the fuel module.
▪▪The cooler is a heat exchanger for the exhaust,
which is connected to the cooling system
▪▪It connects to exhaust manifold and cooling
system via transfer tubes
The purpose of the EGR Cooler is to cool the exhaust
to approximately the same temperature as the engine
coolant before it can enter the EGR valve.
When the cooled inert exhaust gases from the
EGR cooler pass through the EGR valve, they are
mixed with the incoming air/fuel mixture to lower
combustion temperatures and reduce NOx.
EGR Temperature Sensors
An EGR temperature sensor is a thermistor located in
the EGR crossover tube to sense the temperature of
the exhaust entering the EGR valve.
NOTE: This sensor can become coated and
have false readings to the ECM if the EGR
cooler leaks, which allows coolant to flow
into the exhaust chamber.
The EGR temperature sensor is used by the ECM, in
conjunction with the exhaust gas differential pressure
sensor, to calculate the volume of re-circulated
exhaust gases that enter the intake manifold from the
exhaust gas recirculation valve. It also will de-rate
the engine if the EGR temperature is greater than the
engine protection limits.
The EGR Temperature Sensor is a two-wire
thermistor sensor. It determines the temperature of
the exhaust gas coming from the exhaust manifold
in order to determine the amount of flow necessary.
Along with this sensor and the Delta Pressure Sensor,
the ECM uses this information to determine EGR
flow under load and keep flow to a maximum of 30%.
NOTE: When refilling cooling system, always
fill until coolant comes out at bleeder fitting
on top of EGR cooler and/or hose to recovery
tank at top of radiator. Then run engine with
radiator cap off and heater turned on for
10-20 minutes depending on vehicle to make
sure cooling system is free of all air.
▪▪EGR cooler leak issue requires proper bleeding of
system and damage to turbo can result
▪▪DPS ports can fill with water. Blow them out
▪▪Refer to Cummins procedures
EGR Temperature Sensor
Two-wire Thermistor
Module Five

43ISX12-G Fuel Systems
Exhaust Gas System
Electronic EGR Valve
The EGR Valve is controlled by the ECM and
regulates the amount of re-circulated exhaust gases
that enter the intake manifold. The EGR valve lets
some exhaust gases pass into the intake system.
During combustion, these exhaust gases absorb
heat from the burning air and fuel. This lowers peak
combustion temperatures and reduces formation of
oxides of nitrogen, because nitrogen and oxygen
bond under high heat (over 2500 °F) the formation of
NOx is reduced.
When the engine first starts and until it warms up,
the ECM prevents the EGR valve from operating.
When the engine is at operating temperature, the
EGR valve flow is influenced by the position of
the throttle under load. This is generally at light
throttle openings, when a lean mixture could cause
increased oxides of nitrogen. It does not operate at
idle or at wide-open throttle.
Oxides of nitrogen can also be reduced by retarding
ignition timing. This lowers the maximum
temperature reached during combustion. The
maximum ignition-advance setting is then said to be
“emission-limited”.
This is a three-position valve and the ECM manages
this valve by keeping EGR flow from the exhaust
into the mixer at a maximum of 30%. EGR flow only
takes place when the engine is under load and never
at idle. Because of this, the EGR Valve can only be
tested under load or in a stall.
A stuck open EGR valve can result in rough idle or
stalling. A stuck closed EGR valve may produce high
NOx and knocking.
ECM controls the EGR valve with a PWM signal.
This command is based upon the EGR differential
pressure between the exhaust manifold and the mixer
and the temperature.
With a PWM command
signal, the EGR motor
pushes a rod down
against the popper
valve, which is spring
loaded on the bottom.
This action combined
with the three sensors
mounted in different
locations verify the
location of the rod with inputs from the EGR PDS and
the EGR temperature sensor. With this information, it
is able to make constant adjustments to the EGR flow.
EGR Valve and DPS Assembly
3 Poppet EGR
EGR Motors and Position Sensors

44ISX12-G Fuel Systems
The EGR valve has three EGR control motors and
three potentiometers as EGR position sensors. They
all share a 5 volt power supply and the motor return
for a ground. The ECM controls the motors and
receives input from the position sensors.
EGR Position Sensors
There are three EGR motors that move to control the
EGR flow. The EGR valve has three position sensors
inside that confirm the position of the EGR valve
motors to the ECM.
The EGR Valve is controlled by the ECM and
regulates the amount of re-circulated exhaust gases
that enter the intake manifold based on sensor input of
motor rod location, EGR temp sensor and EGR DPS.
The EGR valve position sensors are potentiometers
that sense the position of the EGR valve for the
ECM. They are three-wire potentiometers with a 5
volt reference and the motor return for a ground. The
sensor senses the position of the EGR valve to be in
one of three positions and returns this information
to the ECM, which keeps flow to a maximum of
30% under load. The potentiometers can be tested
manually only when the valve is operating. This valve
cannot be tested unless the vehicle is under load or in
a stall test.
EGR Delta Pressure Sensor
The EGR Delta Pressure Sensor (DPS) compares
the pressure intake differential between the exhaust
manifold and the intake manifold pressures and sends
a signal that is the pressure differential from the two
ports. This DPS can become damaged if the EGR
cooler leaks into the system.
The exhaust gas recirculation differential pressure
sensor is used by the ECM, in conjunction with the
exhaust gas recirculation temperature sensor, to
calculate the volume of re-circulated exhaust gases
that enter the intake manifold from the exhaust gas
recirculation valve. Limits EGR gas to a maximum of
30%.
The EGR DPS has a 5 volt reference, pressure signal
and signal return.
The parameters that are available through INSITE™
for his sensor include;
1. EGR valve flow compensation - It is the control
compensation required to reduce the EGR valve
flow error.
2. EGR valve flow control state - Indicates to the tool
the state of current control of EGR valve. 0 = control
off, 1 = open-loop control, 2 = closed-loop control.
3. EGR valve flow error - Indicates to the tool the
difference between EGR Flow sensed and commanded.
4. EGR valve position commanded - Indicates to the
tool whether the EGR Valve feature is enabled in the
ECM. This parameter is not user adjustable.
5. EGR valve position measured - Position (percent
open) of the EGR Valve after auto zero.
6. EGR valve position sensor signal - Sensor input
voltage detected by ECM.
Module Five

45ISX12-G Fuel Systems
Exhaust Gas System

46ISX12-G Fuel Systems
Activity 1.5:
Understanding EGR Systems
Tools and equipment:
1. Hand Tool Set
Step 1: Using Cummins documentation, determine the following connections.

DPS – 5 Volt Reference ______________ EGR Position Sensor 1: _____________
DPS – Signal wire terminal ____________ EGR Position Sensor 2: _____________
DPS - Sensor return wire terminal _______ EGR Position Sensor 3: _____________
EGR Position Sensor Return: _________
EGR Motor A _________________
EGR Motor B:_________________ EGR Temperature Sensor: ______________
EGR Motor C: ________________ EGR Temperature Sensor Return:_________
EGR Motor Return: _____________

Step 2: Launch INSITE™. Add the following parameters to INSITE™

Engine Speed (RPM) EGR Command
Throttle Plate Position 1 (Percent) DPS Signal Voltage
EGR Flow DPS Pressure
EGR Position Sensor
Step 3: Using the terminals outlined in Step 1, connect DVOM’s to measure (1) DPS voltage drop, (2) Motor
A signals, (3) EGR Position Sensor 1 signals, and (4) EGR Temperature Signal.
Note: Set each meter to record the Min/Max values for each function measured.
Module Five

47ISX12-G Fuel Systems
Step 4: Start and warm-up engine and then follow procedure below to complete the following activities.
Record the signals below noting any changes due to engine speed
DPS DPS EGR EGR EGR
Pressure Voltage Temp Motor A Pos. Sensor A
1. Idle for 30 seconds _______ _______ _____ ________ ___________
2. 1000 rpm for 10 seconds _______ _______ _____ ________ ___________
3. Snap the throttle once (Min) _______ _______ _____ ________ ___________
(Max) _______ _______ _____ ________ ___________
4. Idle for 10 seconds _______ _______ _____ ________ ___________
5. 1500 rpm for 10 seconds _______ _______ _____ ________ ___________
6. Back to idle _______ _______ _____ ________ ___________
Step 5: Did the EGR temperature change during the above procedure? (Y/N):
Step 6: Was there an EGR pressure change throughout the above procedure? (Y/N):
Step 7: Did the EGR valve change through the above procedure? (Y/N):
Optional: (As time allows) Take measurements for Motor B / Position Sensor B and Motor C / Position
Sensor C.
What are your findings?
Exhaust Gas System

48 ISX12-G Fuel Systems
6
Module Six

49ISX12-G Fuel Systems
Base Engine Sensors
Base Engine Sensors
Here is a list of the base engine sensors.
▪▪Engine Coolant Temperature Sensor
▪▪Crankcase Pressure Sensor
▪▪Engine Oil Pressure Sensor
▪▪Engine Oil Temperature Sensor
▪▪Engine Position Sensor (CMP)
▪▪Engine Speed Sensor (CKP)
▪▪Engine Control Module (ECM)
We will be discussing these item by item.
Engine Coolant Temperature
Sensor
The Engine Coolant Temperature sensor is always
threaded into the coolant system so that the sensor
tip is in direct contact with the engine coolant. The
purpose is to sense the temperature of the coolant.
This acts as a choke for fuel enrichment and timing
increases when the engine is cold. If it fails, it can
cause a hard-start or no-start condition in a cold
soaked engine and a rich flooding condition when
warm. This sensor will have a fail-safe backup
strategy in case of failure to reduce these problems.
The coolant temperature sensor’s input to the ECM
is used for engine protection, ignition timing, and
fueling control. When cold, the system adds fuel,
advances timing and increases idle speed. Once it is
warmed up and no longer providing a choke circuit,
the sensor monitors for overheating. If the coolant
temperature is too high, engine de-rate will occur and
possibly lead to engine shutdown.
The thermistor used as an engine Coolant
Temperature sensor is a two-wire sensor with a signal
and a return. Thermistors change resistance as their
temperature changes, which changes the voltage drop
across the fixed resistor inside the ECM. It is checked
by comparing the temperature of the sensor with
voltage and resistance readings.
Engine Crankcase Pressure
Sensor
The Crankcase Pressure sensor is mounted on
the cold side of the rocker arm cover. Its job is to
monitor crankcase pressure. This pressure should be
checked often to confirm that KOEO pressure reads
0 in INSITE™.
The engine Crankcase Pressure sensor monitors
excessive crankcase pressure and reports back to the
ECM. The first stage of alert is a warning, and the
second stage results in engine shutdown usually due
to excessive blowby or malfunction in the engine
ventilation.
Engine Coolant Temperature Sensor

50ISX12-G Fuel Systems
The Crankcase pressure sensor is transducer. It is
a three-wire sensor with a 5 volt reference, return
and signal. Testing the sensor is the same as other
transducers with comparisons to known good units.
Engine Oil Pressure Sensor
The engine oil pressure sensor is threaded into
the side of the block behind the ECM. It senses
engine oil pressure for critical engine protection.
The oil pressure should read 0 psi with the key ON
and engine OFF. A faulty gauge reading can cause
problems if the engine pressure is then lost.
The ECM uses input from the oil pressure sensor
for engine protection. If the oil pressure is too low
engine de-rate and possible shutdown will occur.
Oil pressure sensors are three-wire transducer devices
that run on 5 volts. Testing the sensor involves
verifying the pressure and comparing it to the
pressure signal voltage while using the signal return
for a ground.
Engine Oil Temperature Sensor
The engine oil temperature sensor is threaded into the
side of the block behind the ECM. Its job is to sense
engine oil temperature for critical engine protection.
The engine oil temperature sensor is a two-wire NTC
thermistor with a signal and a return.
The resistance lowers as the temperature rises causing
a voltage drop.
Speed Sensor Types
A speed sensor senses speed of a rotating shaft and
creates a electrical signal that can be interpreted by
the ECM. There are two types of speed sensors:
▪▪Hall-effect Sensor (switch) which produces a
digital on-off signal that is very precise.
▪▪Hall-effect sensors are three-wire sensors and are
used for crank and cam sensing.
▪▪Magnetic Reluctance Sensor which produces an
A/C Signal. These sensors are usually used to
determine vehicle speed and as ABS wheel sensors.
Cold Side of Engine
Oil Pressure Sensor
Module Six

51ISX12-G Fuel Systems
Camshaft Speed/Position Sensor
(EPS)
The Engine Camshaft Speed/Position Sensor is
mounted on the gear housing. The Engine Camshaft
Speed/Position Sensor measures the position of the
engine camshaft by the use of a hall-effect sensor
and seven cast protrusions located on the rear of the
camshaft gear. Whenever the cam gear protrusions
pass the Engine Camshaft Speed/Position Sensor, the
deflection in the sensor flux lines generates a digital
pulse signal to the ECM.
The ECM uses the frequency of the signal resulting
from the six evenly spaced cast protrusions passing
the Engine Camshaft Speed/Position Sensor to
calculate engine speed and, with the Intake Manifold
Pressure/Temperature Sensor input, adjusts the
ignition timing. The ECM recognizes the seventh
signal from the one unevenly spaced protrusion as
the indicator for the start of a new cycle. Each cycle
begins with cylinder #1 as the next cylinder to fire.
The ECM uses this signal to generate the spark
reference signal for the ICM.
The camshaft speed sensor is a hall-effect type sensor
with three wires.
When testing the sensor, check the signal return and
ground. This will be a digital on-off signal that can
be seen with a digital storage oscilloscope and will
increase in frequency on a DVOM as the engine RPM
increases. The voltage will remain fairly constant.
Crankshaft Speed/Position
Sensor (ESS)
Another speed sensor is the engine Crankshaft Speed/
Position sensor, which is mounted at the rear of
the block to measure crankshaft speed. The sensor
measures the position of the engine crank by the use
of a hall-effect sensor and a tone wheel located on
the rear of the crankshaft. Whenever the crank tone-
wheel gear protrusions pass the Engine Crankshaft
Speed/Position Sensor, the deflection in the sensor
flux lines generates a digital pulse to the ECM.
The information from this sensor is used by the ECM
to determine crankshaft rotational speed and position
as a backup to the cam sensor. It is the tachometer
signal used by the computer to recognize the engine
is cranking to turn on the fuel solenoids.
The crankshaft speed sensor is a hall-effect type
sensor with three wires. It does not create electricity,
just turns a circuit on and off.
When testing the sensor, check the signal return and
ground. This will be a digital on-off signal that can
be seen with a digital storage oscilloscope and will
increase in frequency on a DVOM as the engine
RPM increases. The voltage will remain fairly
constant near 2.5v.
Camshaft Speed/Position Sensor
Crankshaft Speed/Position Sensor
Base Engine Sensors

52ISX12-G Fuel Systems
Electronic Control Module
The ECM is the brains (computer) of the system. It
is mounted on the cold side of the engine. Like all
computers, it has inputs that provide information
to the ECM that is in turn used to run the outputs,
which determine the correct fuel mixture, timing,
and boost. Accurate inputs are needed to ensure
correct output commands.
OEM-Installed Sensors
The OEM-installed sensors include;
▪▪Coolant Level Sensor
▪▪Vehicle Speed Sensor
▪▪Accelerator Pedal Position Sensors
▪▪Remote Accelerator Sensor
▪▪Switched Controls
▪▪Warning Lights
Vehicle Speed Sensor
The vehicle speed sensor provides vehicle speed
information to the ECM. This sensor generates a
signal based on the movement of gear teeth from a
gear on the transmission tail shaft. As the gear teeth
pass the sensor, a variable frequency signal
is generated.
The ECM also uses VSS to de-rate and or cut fuel
when customer parameters are set to a certain
road speed.
The vehicle speed sensor is a two-wire sensor that
is a magnetic inductive pickup. It is composed of a
permanent magnet and a coil. When the tone wheel
comes close to the coil during operation, it causes the
magnetic field to shift through, it inducing an A/C
voltage that changes in frequency.
Accelerator Pedal Sensors
These engines use two throttle position sensors
mounted on the accelerator pedal to determine throttle
demand by the driver. Like the Accelerator plate
position, these two sensors are redundant. Earlier
Cummins systems used a single throttle position sensor
and an idle validation switch. Care must be taken to
ensure the correct pedal position sensor is installed.
Electronic Control Module
Accelerator Pedal Sensor
Module Six

53ISX12-G Fuel Systems
The dual hall-effect accelerator pedal is designed
for an accelerator pedal sensor that translates a
position controlled by the operator, into two analog
voltage signals, Accelerator Pedal Sensor 1(APS1)
and Accelerator Pedal Sensor 2 (APS2). The ECM
processes these signals for verification of the
accelerator position. On automotive applications,
this type of interface requires that the pedal, when
released, returns to the idle position via a return
mechanism in the pedal assembly.
The software in the ECM is able to compensate for
variations in the voltage output of the accelerator
pedal component when the pedal is at the idle
position. This ability minimizes the dead band of
the accelerator pedal near the idle position as the
accelerator pedal components age or wear and
eliminates noticeable differences in this dead and due
to normal variations between different accelerator
pedal components. This ability will always enable
the engine to reach 100 percent commanded position,
independent of variations in the accelerator pedal
component. Accelerator Pedal Sensor 1 (APS1) and
Accelerator Pedal Sensor 2 (APS2) have different
position to voltage transfer functions. This allows the
ECM accelerator algorithm to perform an integrity
check of the two signals before outputting a final
commanded accelerator value to the rest of the
system. APS1 has a starting voltage of 1.25 volts and
a wide open throttle voltage of 4.20 volts. APS2 has a
starting voltage of 0.56 volts and a wide open throttle
voltage of 2.06 volts. Note that both sensors start at
two different points and rise together to a wide open
throttle position.
Base Engine Sensors
A fault code will be generated if any of a number of
concerns happen:
▪▪Accelerator pedal position 2 signal circuit shorted
to battery or 5 volt supply,
▪▪Open accelerator pedal return circuit in the
harness or connections,
▪▪Accelerator supply shorted to battery, or failed
accelerator pedal position sensor.

54ISX12-G Fuel Systems
Remote Accelerator Pedal
Assembly
Some vehicles have a remote throttle pedal assembly
located at the rear of the vehicle to aid in remote
engine control for troubleshooting purposes only. A
switch must be thrown on the remote unit to change
from inside to remote operation.
The remote throttle
control is a hall-effect
switch just like in the
accelerator pedal. When
activated, the throttle can
be operated manually
from the rear.
The ECM switches the control for the main and
remote sensors when the interlock switch is on.
▪▪The Accelerator Pedal Position (APP) sensor is
connected to ECM in this application via a three-
wire connector.
▪▪The ECM terminal 29 provides a 5 volt supply to
terminal C of the APP sensor.
▪▪Terminal A of the APP is connected to the ECM
ground at terminal 17, and terminal B of the APP
provides the position signal return data to the
ECM at terminal 30.
Remote Throttle Assembly
Remote Throttle
▪▪The APP can be pinpoint tested using a DVOM or
an oscilloscope.
▪▪The preferred method is to use an oscilloscope
and perform a sweep test. The sweep test
will detect opens, or glitches, that may not be
detectable with the DVOM.
▪▪Normally the APP will return approximately 10%
of the supply voltage at idle, and approximately
90% at wide open throttle.
▪▪As the accelerator pedal is slowly pushed down
the signal return voltage at terminal B of the
sensor will gradually increase from .5v to 4.0V.
▪▪If the accelerator position voltage is determined
to be out of range by the GCM a code 18 will be
set and the engine will idle.
▪▪The override switch will provide limp home
operation of the system.
Module Six

55ISX12-G Fuel Systems
Activity 1.6:
Testing and Verifying Position Sensors
Cam Speed/Position Sensor
Tools and equipment:
1. Cummins wiring diagram 2. Hand Tool Set 3. DVOM 4. INSITE™
Step 1: Using the repair manual, locate the Cam Speed/Position sensor wiring diagram:
CS/P 5 volt supply Wire terminal _______________________
CS/P Signal Return Wire terminal _______________________
CS/P Sensor Signal Wire terminal _______________________
Step 2:
Do the wire terminals of the wiring diagram and the harness coincide? YES Or NO
Step 3:
Back probe the CS/P and perform the following exercise.
With the engine running record the following data:
Idle - DVOM/DC Voltage ___________________________ Frequency __________________
1500 RPM - DVOM/DC Voltage _______________________ Frequency __________________
Step 4:
Disconnect the CS/P Sensor with KOER
Will the engine continue to run without the CS/P? Yes or No _________________
If the engine quit running, try and restart. If the engine kept running, shut off and restart. What were your
findings? _________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
Reconnect the CS/P Sensor if it is still disconnected
Step 5: What are the codes associated with this CS/P? __________________________________
If the CS/P was defective what would the INSITE™ display? ________________________________
Base Engine Sensors

56ISX12-G Fuel Systems
Activity 1.6:
Testing and Verifying Position Sensors
Crank Speed/Position Sensor
Tools and equipment:
1. Cummins Troubleshooting and Repair Manual 2. Hand Tool Set 3. DVOM
Step 1: Using the repair manual, locate the Crank Speed/Position sensor wiring diagram:
CS/P 5 volt supply Wire terminal _______________________
CS/P Signal Return Wire terminal _______________________
CS/P Sensor Signal Wire terminal _______________________
Step 2:
Do the wire terminals of the wiring diagram and the harness coincide? YES or NO
Step 3:
Back probe the CS/P and perform the following exercise.
With the engine running record the following data:
Idle - DVOM/DC Voltage ___________________________ Frequency __________________
1500 RPM - DVOM/DC Voltage ______________________ Frequency ___________________
Step 4:
Disconnect the CS/P Sensor with KOER
Will the engine continue to run without the CS/P? Yes or No _________________
If the engine quit running, try and restart. If the engine kept running, shut off and restart. What were your
findings? _________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
Reconnect the CS/P Sensor if it is still disconnected
Step 5: What are the codes associated with this CS/P? __________________________________
If the CS/P was defective what would the INSITE™ display? ________________________________
__
Module Six

57ISX12-G Fuel Systems
Activity 1.6:
Testing and Verifying Position Sensors
Accelerator Pedal Position Sensors 1 & 2
Tools and equipment:
1. Cummins Troubleshooting and Repair Manual 2. INSITE™ (optional)
3. Hand Tool Set 4. DVOM
Step 1: Using the repair manual locate the APPS wiring diagram
APPS Sensor 1 Return Wire terminal _______________
APPS Sensor 1 Signal Wire terminal _______________
APPS Sensor 1 5-volt Reference Wire terminal ______________
APPS Sensor 2 Return Wire terminal _______________
APPS Sensor 2 Signal Wire terminal _______________
APPS Sensor 2 5-volt Reference Wire terminal ______________
Does it have an Idle Validation Switch? Yes or No
Step 2:
Visually locate APPS sensor and identify the wiring harness.
Do the wire terminals of the wiring diagram and harness coincide? Yes or No
Step 3:
Using two DVOMs connect the positive lead to APPS Signal wire for sensors 1 & 2, record the following mea-
surements: KEY ON ENGINE OFF (KOEO)
Without depressing the accelerator pedal, what is the APPS sensor signal voltage? 1_____ 2_____
Depress the accelerator pedal 50%, what is the APP sensor signal voltage? 1 ____ 2_____
Fully depress the accelerator pedal. What is the APP sensor signal voltage? 1_____ 2_____
Step 4:
Using parameter ID from INSITE™ for APPS 1 & 2, record the following measurements:
KEY ON ENGINE OFF (KOEO)
Without depressing the accelerator pedal, what is the APP sensor signal voltage? 1_____ 2 ______
Depress the accelerator pedal 50%, what is the APP sensor signal voltage? 1 _____ 2 ______
Fully depress the accelerator pedal. What is the APP sensor signal voltage? 1 _____ 2 ______
Is the voltage on APP1 and APP2 the same? Yes or No
If they are different, how are they different and what is the relationship? ________________________
What are the faults associated with the Accelerator Pedal Sensors?____________________________
Base Engine Sensors

58ISX12-G Fuel Systems
Coolant Level Sensor
The coolant level sensor is mounted in the reservoir to
monitor coolant level. It is a capacitance style sensor.
When the coolant level drops, it signals the ECM.
The coolant level sensor monitors coolant level.
When the coolant level drops below a certain level
the ECM will de-rate the engine. The level of
de-rate becomes greater with time if the problem
is not corrected. The ECM will use this input to
de-rate or shutdown the engine depending on
customer parameters.
The engine coolant level sensor is a capacitance type
sensor that works by changing capacitance on a wire
that is immersed in the fluid. It must be mounted
vertical when replaced and has a different testing
procedure than switches or resistance sensors. The
sensor can leak internally, shorting the connector
pins, causing stalls, de-rated power etc.
Switched ECM Inputs
There are various switched inputs to the vehicle ECM
to provide operator requested commands. These
include PTO parameters and feature adjustment
control. Many of these items are accessories or special
features that may not be present on the vehicle.
The switched inputs include several on/off switches
like:
▪▪Override normal throttle operations
▪▪Operate requested accessories
▪▪Prevent starter motor operation without clutch
depress
▪▪Override cooling fan automatic operation
▪▪Enter diagnostic functions
Switched inputs are pulled low to engage so the ECM
sees the voltage change on the line from high to low.
Coolant Level Sensor
Switched Inputs
Module Six

59ISX12-G Fuel Systems
Warning and Indicator Lamps
This engine has three lamps to alert/notify the driver
of problems.
▪▪Yellow lamp – Warning lamp illuminates with
some fault codes and pending items
▪▪Red – Stop lamp warns of pending shutdown and
serious faults needing attention
▪▪Blue – Maintenance required lamp
Data and Control Signals
There are many outputs from the ECM that are used
to control engine functions. These include:
▪▪CAN Data communications
▪▪Starter lockout signal
▪▪Fan Control signal
CAN, J1939 & J1587 Data Bus
(Communications)
The CAN Data Bus Parameters are available for
network communications. They are broadcasted by
the ECM and are internal to the engine body and
wiring harness.
▪▪The J1939 datalink. The INSITE™ diagnostic
tool can be connected to this datalink to
communicate with the ECM.
▪▪J1587 communications for OEM systems
including engine. This line is slower than the
1939.
▪▪Diagnostic tool interface provided at engine and
other location based on OEM application.
▪▪Twisted-pairs of wires to reduce Electromagnetic
Interference and Radio Frequency Interference
(EMI & RFI).
▪▪120 Ω terminating resistors to provide proper
electrical load to circuit and to determine the start
and end of the network connections.
The network protocol is used to communicate
with other networked controllers. Several different
protocols are utilized depending upon the speed
of transmission needed for the component being
monitored. Some components use the lower priority
protocols as the reduced baud rate is not important.
Other items require higher speeds to operate properly.
You should only use J1939 Protocol on the engine for
fastest updating with the INSITE™ service tool.
The CAN networks communications system can
have several protocols. Testing the system involves
checking the wiring for continuity and using
INSITE™ to check the communications.
Base Engine Sensors

60 ISX12-G Fuel Systems
7
Module Seven

61ISX12-G Fuel Systems
Ignition System Components
This ignition system components include;
▪▪Coil-On-Plug (COP) Ignition Coils
▪▪Knock Sensors 1 & 2
▪▪Ignition Control Module
▪▪Spark Plugs
Combustion Knock Sensors 1 & 2
Two major knock sensor designs are used today:
broadband single-wire and flat response two-wire
knock sensors. Both types are piezoelectric crystals
like the old crystal earphones and microphones that
send voltage and frequency signals to the ECM that
detects engine noise caused by detonation. This
engine has two knock sensors, each sensor monitors
three cylinders. The location of the knock sensors
is specific and the knock detection is calibrated for
this position, therefore, knock sensors must not be
repositioned from the original location.
The ECM has three thresholds programmed into it for
knock detection and prevention.
When detonation is sensed, the ECM retards engine
timing until detonation is diminished. Over time,
the ECM will attempt to restore normal timing if
detonation diminishes.
Light Knock: Lowest of the three thresholds, is
designed to guard against damage from light to
mild knock. The ECM will retard ignition timing
and slightly de-rate the throttle. A yellow lamp will
illuminate to warn the operator that light knock has
been detected.
Heavy Knock: This warning will be activated if the
light knock protection fails to eliminate the problem
or a knock is detected that crosses the heavy knock
threshold. The ECM will trigger a severe throttle de-
rate and illuminate the red warning lamp.
Cold Knock Threshold: This provides severe
protection while the engine is reaching a stable
operating temperature. Time at this threshold is
a function of coolant temperature at startup. The
cold knock threshold is disabled when the engine
temperature reaches 160°F (71°C).
▪▪The knock sensors are located near the front and
rear of the engine.
▪▪The front knock sensor listens to cylinders 1,2,3
for detonation.
▪▪The rear knock sensor listen to cylinders 4,5,6 for
detonation.
Ignition System Component

62ISX12-G Fuel Systems
Module Seven
Combustion Knock Sensor 1
These are what’s called “piezoelectric” devices.
When the gallium crystal vibrates at a specific
frequency that is associated with engine detonation
noise it resonates and produces a small amount of AC
current. This is a very weak signal and only high-end
oscilloscopes may be able to display it. INSITE™
parameter display is probably the best way to see if it
is working.
An ohmmeter can be used to check continuity.
Detonation can be monitored with INSITE™ or you
can create a simulated knock and monitor with an
oscilloscope or DVOM with a frequency function.
Combustion Knock Sensors 2
Both sensors work the same and are tested the same.
Care must be taken to eliminate other sources of
knock such as noise caused by improper timing of
the compressor.
Combustion Knock Control
Systems
A knock sensor’s common pattern is an alternating
signal (AC) with the frequency changing to match
the noise of the knock. It is sometimes very weak and
often difficult to monitor on a conventional lab scope.
PICO Scopes are more effective to see weak signals
as they can amplify the trace. A DVOM must have
the proper frequency range to pick up the signal.
Knock Sensor 2
Knock Sensor 1

63ISX12-G Fuel Systems
Ignition System Component
ICM Spark Voltage & Misfire
Signals
The ICM has a built-in engine ignition diagnostic
capability. The ICM monitors individual spark
plug voltage and misfires and reports it to the ECM
as an input for diagnostic purposes only. Ignition
timing and air/fuel mixture values are not affected
by these signals.
The ICM provides kV and misfire detection as an
input to the ECM for diagnostic fault code capability.
This engine incorporates multiple spark discharge
technology that uses solid state devices to trigger the
capacitor charge/discharge cycle very rapidly when
the engine has low intake manifold pressure. During
this condition, there is a relatively small amount of
air/fuel mixture in the cylinder, and the cylinder is
relatively cool. It is possible for the flame created
by the spark to extinguish, due to the low heat and
sparse air/fuel mixture in the cylinder. Misfires
can send unburned fuel and oxygen to the catalytic
converter, overheating it and damaging the substrate.
Any misfires should be addressed to prevent this
damage from occurring.
Testing can only be done on the primary side or
with INSITE™. Primary resistance can be tested as
well as the secondary windings for shorts to ground
with an ohmmeter.
CAUTION: Misfires can damage the catalyst
which can be very expensive. Cylinder
balance tests have been eliminated from
INSITE™ to prevent this.
Coil On Plug Ignition
This engine uses a coil-on-plug type of ignition coil.
This coil mounts directly to the spark plug. The high
voltage pulse from the secondary windings of the coil
are delivered directly to the spark plug. This system
eliminates traditional spark plug wires resulting in
less maintenance and a more efficient transfer of
electrical energy from the coil to the plug.
The ECM requires an initial input from the
Camshaft Speed Position Sensor for the engine to
start. Once the ECM gets synchronization from this
sensor and the Crankshaft Speed Position Sensor,
the Crankshaft Speed Position sensor becomes
the primary input for ignition timing. The ECM
also uses input from the Intake Manifold Pressure
Temperature Sensor to adjust how far to advance the
timing of the spark.
To determine if an ignition coil is operational and
producing the high voltage required to create a spark
at the plug, an approved ignition coil spark tester
is recommended. For the ISX12G engine, the COP
must be kept nearly vertical during operation due
to oil-filled cooling of the coil. The test kit adapter
must be used to properly position the COP during
Coil-on-Plug Ignition

64ISX12-G Fuel Systems
Spark plugs work very hard to do their job and are
under appreciated. At 2000 rpm, one plug is firing
more than 16 times per second regardless of the load
on the engine. The plugs do wear out and will misfire
under a load as well. This puts a lot of stress on a plug
over its intended life so maintenance intervals are
approximate only. The use of proper plugs torqued to
the proper spec will help this interval.
A general rule for plugs is: when in doubt, change
them out.
Module Seven
spark testing on this engine. When using this tester, no attempt should be made to adjust the tester. The
ignition coil tester is preset and is not adjustable.
Attempts to adjust the tester will damage the tool.
The secondary winding measurement for the COP
resistance is taken between the spark plug connection
and either pins B or C of the 4 pin connector for the
CM2180A ECM.
The engine camshaft speed/position sensor provides
engine speed and cylinder #1 compression stroke
information to the ECM. This sensor generates a
signal from the passing of seven cast protrusions
located on the rear of the camshaft gear. An engine
crankshaft position sensor mounted at the rear of
the block is used to signal piston position during
the stroke. Both of the ISX12G position sensors are
hall-effect type and provide a DC high-low (5 to 0V)
signal to the ECM. The engine crankshaft speed/
position sensor is located on top of the flywheel
housing. The information from this sensor is used by
the ECM to determine crankshaft rotational speed and
each cylinder’s piston position as it relates to degrees
of crankshaft rotation.
The plugs used on the 12L are made with an
Iridium center for best life in the harsh heavy duty
environment. These plugs have to dissipate the dry
hotter heat created by natural gas.
Never use a socket with a rubber retainer insert. The
rubber insert can leave a residue on the plug porcelain
and lead to carbon tracking. Use a magnetic plug
socket such as the Snap-On #S9706KMAG. Plugs
should never be re-gapped as the coating on the
electrodes will be damaged. Clean plugs, socket with
denatured alcohol and torque to (28 ft. lbs.). This is
critical for proper plug life.
Coil-on-Plug Assembly

65ISX12-G Fuel Systems
Activity 1.7:
Ignition System Maintenance
Tools and equipment:
1. Hand Tool Set
Procedures: In this lab, we will use the Cummins procedures for removing, installing, and torqueing spark
plugs as outlined by Cummins. These procedures include:
▪▪ Never touch plug
▪▪ Clean with denatured alcohol
▪▪ Use clean socket
▪▪ Do not gap or re-gap plugs
▪▪ Torque specs very critical--28-32 ft lbs.
▪▪ Replace according to TSB Maintenance Schedule
Step 1: Remove the connector from the COP on cylinder #6
Step 2: Remove the COP on cylinder #6
Properly clean, reinstall and torque.
Ignition System Component

Tests
ISX12-G Fuel Systems
Post Test
Cummins ISX 12-G Fuel Safety Level 1
1. The Cummins ISX 12L engine can only run on CNG and not LNG? (T/F)
2. A Fuel Control Valve is similar to a fuel injector? (T/F)
3. The Cummins ISX engine is a Speed Density system versus a Mass Air Flow System like the
8.9L ISL-G? (T/F)
4. The EGR Valve has only two positions? (T/F)
5. The Cummins ISX 12L engine has a knock sensor for each cylinder? (T/F)
6. The EGR Delta Pressure Sensor calculates EGR Flow? (T/F)
7. There are three different types of Speed Sensors? (T/F)
8. What best describes best practice for replacing spark plugs in a Cummins ISX engine?
a. Clean the old dielectric grease from the spring connection with a lint-free cloth
b. Wipe the ceramic portions of the spark plug with alcohol after handling
c. Replace the rubber boot with a new one included when buying spark plugs
d. All of these are considered best practice for replacing spark plug

67ISX12-d Fuel Systems

ISX12-G Fuel Systems
TOXICITY: Nontoxic, it is not a poison like Carbon
Monoxide but it does displace Oxygen.
FLAMMABILITY: Flammability range is narrow
5-15% - below 5 is too lean to burn, above 15
too rich. Edges of a cloud could be right mixture.
Heaters and other spark producing items must be
relocated.
VENTILATION: Must be trapped vertically to
be dangerous--- look up for traps at ceiling/false
ceilings etc. Lighter than air so most shops are
equipped with auto vents on the methane detection
circuit.
LEAK DETECTION: Mercaptin NOT present in
LNG unless infused so it will have no odor. Methane
detectors and hand held combustible gas detectors
available along with commercial bubble style leak
detectors. CG detectors will go off on many
substances such as glycol, silicone, diesel, hyd. Fluid
so it is just a gross indicator.
Natural Gas Safety Considerations
COLLISION: Cylinders must have a Detailed
Visual Inspection and hardware should be carefully
inspected for damage. Cylinders should be closed
and ¼ turn valve closed if vehicle is involved in an
accident.
STORAGE: LNG vehicles should be stored outside
due to venting of tank. CNG system is sealed and
will not leak to atmosphere.
SHOP SAFETY/EQUIPMENT: Methane detectors
and ceiling ventilation should be reviewed by
engineering. Special tools kit being provided to
perform defueling etc.

69ISX12-d Fuel Systems

References
Sources:
Compressed Gas Association
1725 Jefferson Davis Highway,
#1004 Arlington, VA 22202-4102
Telephone: 703-412-0900
Gas Research Institute
8600 W. Bryn Mawr Avenue
Chicago, IL 60631-3652
Telephone: 773-399-8352
American National Standards Institute
11 W. 42nd Street
New York, NY 10036
Telephone: 212-642-4900
National Fire Protection Association
11 Tracy Drive
Avon, MA 02322
Telephone: 800-593-6372
Natural Gas Vehicle Coalition
1515 Wilson Blvd. Suite 1030
Arlington, VA 22209
Telephone: 703-527-3022
Department of Transportation
400 Seventh Street, SW
Washington, DC 20590
Telephone: 202-366-4000
Publications:
CGA C-6.4, “Methods for External Visual
Inspection of Natural Gas Vehicle Fuel
Containers and Their Installations,” 1st
Edition (1997)
NFPA 52, “Standards for Compressed
Natural Gas Vehicular Fuel Systems”
National Fire Protection Association,
1 Batterymarch Park, Box 9101, Quincy, MA
02269-9101
ANSI/AGA-NGV2, “ Basic Requirements for
Compressed Natural Gas Vehicle Fuel
Containers,” American Gas Association
Laboratories, 8501 East Pleasant Valley
Road, Cleveland, OH 44131
FMVSS304, “Compressed Natural Gas Fuel
Container Integrity,” Federal Motor Vehicle
Safety Standards, US DOT, NHTSA
Gas Research Institute, “ Natural Gas
Vehicle Cylinder Care and Maintenance
Handbook” (1997)
CHP Title 13
ISX12-G Fuel Systems

71ISX12-d Fuel Systems

72 ISX12-G Fuel Systems
Notes

73ISX12-G Fuel Systems
Notes

74 ISX12-G Fuel Systems
Notes

75ISX12-G Fuel Systems
Notes

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