
Symptom:
SYSTEM UNDERVOLTAGE
When Monitored and Set Condition:
SYSTEM UNDERVOLTAGE
When Monitored: Ignition on. The CAB monitors the Fused Ignition Switch Output
circuit voltage above 10 km/h (6 mph) every 7 milliseconds for proper system voltage.
Set Condition: If the voltage is below 9.5 volts, the Diagnostic Trouble Code (DTC) is set.
POSSIBLE CAUSES
BATTERY VOLTAGE LOW
INTERMITTENT DTC
FUSED IGNITION SWITCH OUTPUT CIRCUIT HIGH RESISTANCE
CAB - INTERNAL FAULT
TEST ACTION APPLICABILITY
1 Turn the ignition on.
With the DRBIIIt, erase DTC's.
Turn the ignition off.
Turn the ignition on.
Start the engine.
Drive the vehicle above 16 km/h (10 mph) for at least 20 seconds.
Stop the vehicle
With the DRBIIIt, read DTC's.
Does the DRBIIItdisplay System Undervoltage DTC?All
Ye s®Go To 2
No®Go To 5
2 Engine Running.
Measure the battery voltage.
Is the battery voltage below 10 volts?All
Ye s®Refer to appropriate service information for charging system
testing and repair.
Perform ABS VERIFICATION TEST - VER 1.
No®Go To 3
3 Disconnect the CAB harness connector.
Turn the ignition on.
Measure the voltage of the Fused Ignition Switch circuit.
Is the voltage above 10 volts?All
Ye s®Go To 4
No®Repair the Fused Ignition Switch Output Circuit for high resis-
tance
Perform ABS VERIFICATION TEST - VER 1.
30
BRAKES (CAB)

TEST ACTION APPLICABILITY
4 Turn the ignition off.
Disconnect the TRAC OFF Switch harness connector.
Disconnect the CAB harness connector.
Turn the ignition on.
Check the TRAC OFF Switch Sense circuit for short to B+ and for an open.
Is the Sense circuit shorted or open?All
Ye s®Repair the TRAC OFF Switch Sense circuit for a short to battery
or for an open.
Perform ABS VERIFICATION TEST - VER 1.
No®Replace the Body Control Module in accordance with the Service
Information.
Perform ABS VERIFICATION TEST - VER 1.
5 Turn the ignition off.
NOTE: The purpose of this test is to perform the Instrument Cluster self
test.
Depress and hold the Odometer Reset Button.
Turn the Key from OFF to ON and then back to OFF.
Release the Odometer Reset Button.
Do the Instrument Cluster Indicators and Gauges activate and deactivate?All
Ye s®Replace the Body Control Module in accordance with the Service
Information.
Perform ABS VERIFICATION TEST - VER 1.
No®Replace the Instrument Cluster in accordance with the Service
Information.
Perform ABS VERIFICATION TEST - VER 1.
6NOTE: The purpose of this test is to perform the Instrument Cluster self
test.
Depress and hold the Odometer Reset Button.
Turn the Key from OFF to ON and then back to OFF.
Release the Odometer Reset Button.
Do the Instrument Cluster Indicators and Gauges activate and deactivate?All
Ye s®Go To 7
No®Replace the Instrument Cluster in accordance with the Service
Information.
Perform ABS VERIFICATION TEST - VER 1.
7 Turn the ignition off.
Disconnect the TRAC OFF Switch harness connector.
Turn the ignition on.
Does the TRAC OFF Indicator light and then go out?All
Ye s®Replace the TRAC OFF switch.
Perform ABS VERIFICATION TEST - VER 1.
No®Go To 8
37
BRAKES (CAB)
*TRAC OFF INDICATOR NEVER/ALWAYS ON ÐContinued

Verification Tests
ABS VERIFICATION TEST - VER 1 APPLICABILITY
1. Turn the ignition off.
2. Connect all previously disconnected components and connectors.
3. Ensure all accessories are turned off and the battery is fully charged.
4. Ensure that the Ignition is on, and with the DRBIII, erase all Diagnostic Trouble Codes from
ALL modules. Start the engine and allow it to run for 2 minutes and fully operate the system
that was malfunctioning.
5. Turn the ignition off and wait 5 seconds. Turn the ignition on and using the DRBIII, read
DTC's from ALL modules.
6. If any Diagnostic Trouble Codes are present, return to Symptom list and troubleshoot new
or recurring symptom.
7. If there are no DTC's present after turning ignition on, road test the vehicle for at least 5
minutes. Perform several antilock braking stops.
8. Caution: Ensure braking capability is available before road testing.
9. Again, with the DRBIIItread DTC's. If any DTC's are present, return to Symptom list.
10. If there are no Diagnostic Trouble Codes (DTC's) present, and the customer's concern can
no longer be duplicated, the repair is complete.
Are any DTC's present or is the original concern still present?All
Ye s®Repair is not complete, refer to appropriate symptom.
No®Repair is complete.
40
VERIFICATION TESTS

FUSES (IPM)FUSE
NO.AMPS FUSED CIRCUIT FUNCTION
1 20A INTERNAL FUSED B(+)
2 15A INTERNAL FUSED PARK LAMP RELAY OUTPUT
3 15A INTERNAL FUSED PARK LAMP RELAY OUTPUT
4 30A INTERNAL FUSED B(+)
5 20A F306 16DB/PK FUSED ACCESSORY RELAY OUTPUT
6 20A F307 16LB/PK (BATTERY POSITION) FUSED B(+)
6 20A F307 16LB/PK (ACCESSORY RELAY POSITION) FUSED ACCESSORY RELAY OUTPUT
8 20A INTERNAL FUSED B(+)
9 40A INTERNAL FUSED B(+)
10 40A C7 12DB FUSED FRONT BLOWER MOTOR RELAY OUTPUT
11 20A F302 18GY/PK FUSED ACCESSORY RELAY OUTPUT
12 25A C51 12LB/BR FUSED REAR BLOWER MOTOR RELAY OUTPUT
13 40A C15 12DB/WT FUSED REAR WINDOW DEFOGGER RELAY OUTPUT
14 15A INTERNAL FUSED B(+) (I.O.D.)
15 20A INTERNAL FUSED B(+)
16 25A INTERNAL FUSED B(+)
17 20A INTERNAL FUSED B(+)
18 15A INTERNAL FUSED B(+)
19 40A A101 12VT/RD FUSED B(+)
20 40A A102 12WT/RD FUSED B(+)
21 25A A111 12DG/RD FUSED B(+)
22 40A A110 12OR/RD FUSED B(+)
23 10A A106 20LB/RD FUSED B(+)
24 20A A701 16BR/RD FUSED B(+) (HAZARD)
26 20A A103 18GY/RD FUSED B(+)
27 40A A112 12OR/RD FUSED B(+)
28 40A F30 12PK/YL FUSED ACCESSORY RELAY OUTPUT
30 40A SPARE SPARE
31 40A A113 12WT/RD FUSED B(+)
32 40A A115 12YL/RD FUSED B(+)
33 15A INTERNAL FUSED ACCESSORY RELAY OUTPUT
C
O
N
N
E
C
T
O
R
P
I
N
O
U
T
S
51
CONNECTOR PINOUTS

TABLE OF CONTENTS - Continued
P0235-BOOST PRESSURE SENSOR SIGNAL VOLTAGE TOO LOW.............67
P0235-BOOST PRESSURE SENSOR SUPPLY VOLTAGE TOO HIGH OR LOW....70
P0335-CKP POSITION SENSOR CIRCUIT OVERSPEED RECOGNITION.........73
P0340-CKP POSITION SENSOR CIRCUIT DYNAMIC PLAUSIBILITY.............75
P0340-CMP POSITION SENSOR CIRCUIT CMP/CKP SYNC FAILURE...........77
P0340-CMP POSITION SENSOR CIRCUIT SIGNAL FREQUENCY TOO HIGH.....80
P0340-CMP POSITION SENSOR CIRCUIT STATIC PLAUSIBILITY...............80
P0380-GLOW PLUG CIRCUIT A OPEN CIRCUIT.............................84
P0380-GLOW PLUG CIRCUIT A SHORT CIRCUIT............................84
P0403-EGR SOLENOID CIRCUIT OPEN CIRCUIT............................87
P0403-EGR SOLENOID CIRCUIT SHORT CIRCUIT...........................90
P0480-FAN 1 CONTROL CIRCUIT OPEN CIRCUIT...........................92
P0480-FAN 1 CONTROL CIRCUIT SHORT CIRCUIT..........................94
P0481-FAN 2 CONTROL CIRCUIT OPEN CIRCUIT...........................96
P0481-FAN 2 CONTROL CIRCUIT SHORT CIRCUIT..........................98
P0500-VEHICLE SPEED SENSOR FREQUENCY TOO HIGH..................100
P0500-VEHICLE SPEED SENSOR HIGH LEVEL DURATION...................100
P0500-VEHICLE SPEED SENSOR PLAUSIBILITY...........................100
P0500-VEHICLE SPEED SENSOR SIGNAL VOLTAGE TOO HIGH..............100
P0514-BATTERY TEMP SENSOR CIRCUIT SIGNAL VOLTAGE TOO HIGH.......104
P0520- OIL PRESS SENSOR CIRCUIT MALF PLAUSIBILITY..................107
P0520-OIL PRESS SENSOR CKT MALF SUPPLY VOLTAGE TOO HIGH OR LOW .110
P0530-A/C PRESSURE SENSOR CIRCUIT PLAUSIBILITY....................112
P0530-A/C PRESSURE SENSOR CIRCUIT SIGNAL VOLTAGE TOO HIGH.......112
P0530-A/C PRESSURE SENSOR CIRCUIT SIGNAL VOLTAGE TOO LOW.......112
P0530-A/C PRESSURE SENSOR CIRCUIT SUPPLY VOLTAGE TOO HIGH OR
LOW.................................................................112
P0560-SYSTEM VOLTAGE TOO HIGH.....................................117
P0560-SYSTEM VOLTAGE TOO LOW.....................................120
*CHECKING THE CHARGING SYSTEM OPERATION - DIESEL................120
P0615-STARTER RELAY CIRCUIT SHORT CIRCUIT.........................124
P0620-GENERATOR FIELD CONTROL MALF BATTERY VOLTAGE
DEVIATION TOO HIGH.................................................126
P0620-GENERATOR FIELD CONTROL MALF BATTERY VOLTAGE
DEVIATION TOO LOW..................................................126
P0620-GENERATOR FIELD CONTROL MALF BATTERY VOLTAGE TOO HIGH . . .126
P0620-GENERATOR FIELD CONTROL MALF BATTERY VOLTAGE TOO LOW. . . .126
P0620-GENERATOR FIELD CONTROL MALF CHARGING VOLTS TOO LOW. . . .126
P0620-GENERATOR FIELD CONTROL MALF OPEN CIRCUIT.................126
P0620-GENERATOR FIELD CONTROL MALF SHORT CIRCUIT................126
P0620-GENERATOR FIELD CONTROL MALF UNSTABLE CURRENT...........126
P0627-FUEL LIFT PUMP RELAY CONTROL CIRCUIT OPEN CIRCUIT..........129
P0627-FUEL LIFT PUMP RELAY CONTROL CIRCUIT SHORT CIRCUIT.........131
P0641-SENSOR REFERENCE VOLTAGE A CKT VOLTAGE TOO HIGH..........133
P0651-SENSOR REFERENCE VOLTAGE B CKT VOLTAGE TOO HIGH..........133
P0641-SENSOR REFERENCE VOLTAGE A CKT VOLTAGE TOO LOW..........136
P0651-SENSOR REFERENCE VOLTAGE B CKT VOLTAGE TOO LOW..........136
P0645-A/C CLUTCH RELAY CIRCUIT OPEN CIRCUIT........................139
P0645-A/C CLUTCH RELAY CIRCUIT SHORT CIRCUIT......................142
P0685-ECM/PCM RELAY CONTROL CIRCUIT SHUTS OFF TOO EARLY........145
P0685-ECM/PCM RELAY CONTROL CIRCUIT SHUTS OFF TOO LATE..........147
P0703-BRAKE SWITCH SIGNAL CIRCUITS PLAUSIBILITY WITH
REDUNDANT CONTACT................................................149
iii

TABLE OF CONTENTS - Continued
P0703-BRAKE SWITCH SIGNAL CKTS PLAUS W/REDUNDANT CONTACT
AFTER INITIALIZATION.................................................149
P0833-CLUTCH PEDAL PLAUSIBILITY....................................153
P1130-FUEL RAIL PRESSURE MALFUNCTION LEAKAGE DETECTED..........155
P1130-FUEL RAIL PRESSURE MALFUNCTION PRESSURE TOO HIGH-SHUT
OFF .................................................................155
P1130-FUEL RAIL PRESSURE MALFUNCTION PRESSURE TOO LOW.........155
P1130-FUEL RAIL PRESSURE MALFUNCTION SOLENOID OPEN.............155
P1131-FUEL PRESSURE SOLENOID OPEN CIRCUIT........................158
P1131-FUEL PRESSURE SOLENOID PLAUSIBILITY IN AFTER-RUN............158
P1131-FUEL PRESSURE SOLENOID SHORT CIRCUIT.......................158
P1511-BATTERY SENSE LINE 1 VOLTAGE TOO HIGH.......................162
P1511-BATTERY SENSE LINE 1 VOLTAGE TOO LOW.......................164
P1605-IGNITION SWITCH PLAUSIBILITY..................................166
P1685-SKIM SYSTEM INVALID KEY CODE RECEIVED.......................168
P1685-SKIM SYSTEM INVALID SECRET KEY IN EEPROM....................168
P1685-SKIM SYSTEM KEY COMMUNICATION TIMED OUT...................168
P1685-SKIM SYSTEM SKIM ERROR......................................168
P1685-SKIM SYSTEM WRITE ACCESS TO EEPROM FAILURE................168
P2120-ACC PEDAL POSITION SENSOR 1 CKT PLAUSIBILITY................170
P2120-ACC PEDAL POSITION SENSOR 1 CKT PLAUSIBILITY WITH BRAKE
SWITCH..............................................................170
P2120-ACC PEDAL POSITION SENSOR 1 CKT PLAUSIBILITY WITH
POTENTIOMETER.....................................................170
P2120-ACC PEDAL POSITION SENSOR 1 CKT SIGNAL VOLTAGE TOO HIGH . . .170
P2120-ACC PEDAL POSITION SENSOR 1 CKT SIGNAL VOLTAGE TOO LOW . . .170
P2120-ACC PEDAL POSITION SENSOR 1 CKT SUPPLY VOLTAGE TOO
HIGH OR LOW........................................................170
*CHECKING THE A/C CLUTCH OPERATION...............................179
*CHECKING THE ACCELERATOR PEDAL POSITION SENSOR CALIBRATION . . .181
*CHECKING THE BOOST PRESSURE SENSOR CALIBRATION................182
*CHECKING THE ECM POWER AND GROUND CIRCUITS....................183
*CHECKING THE EGR SYSTEM..........................................185
*CHECKING THE ELECTRIC RADIATOR FAN OPERATION...................186
*CHECKING THE ENGINE COOLANT TEMPERATURE SENSOR CALIBRATION . .193
*CHECKING THE ENGINE MECHANICAL SYSTEMS.........................194
*CHECKING THE GLOW PLUG OPERATION...............................195
*CHECKING THE LIFT PUMP MOTOR OPERATION.........................197
*CHECKING THE MAF SENSOR CALIBRATION.............................200
*CHECKING THE SPEED CONTROL OPERATION...........................201
*CHECKING THE VEHICLE SPEED SIGNAL................................204
*ENGINE CRANKS BUT WILL NOT START.................................207
*ENGINE WILL NOT CRANK.............................................210
VEHICLE THEFT/SECURITY
ANTENNA FAILURE....................................................214
COP FAILURE.........................................................214
EEPROM FAILURE.....................................................214
INTERNAL FAULT......................................................214
RAM FAILURE.........................................................214
SERIAL LINK INTERNAL FAULT..........................................214
STACK OVERFLOW FAILURE............................................214
PCM STATUS FAILURE.................................................216
iv

TABLE OF CONTENTS - Continued
SERIAL LINK EXTERNAL FAULT.........................................216
ROLLING CODE FAILURE...............................................218
VIN MISMATCH........................................................218
TRANSPONDER COMMUNICATION FAILURE..............................220
TRANSPONDER CYCLIC REDUNDANCY CHECK (CRC) FAILURE.............220
TRANSPONDER ID MISMATCH..........................................220
TRANSPONDER RESPONSE MISMATCH..................................220
VERIFICATION TESTS
VERIFICATION TESTS..................................................223
8.0 COMPONENT LOCATIONS..............................................227
8.1CONTROL MODULES.............................................227
8.2CONTROLS AND SOLENOIDS......................................227
8.3DATA LINK CONNECTOR..........................................227
8.4FUEL SYSTEM...................................................228
8.5RELAYS.........................................................228
8.6SENSORS.......................................................229
8.7SWITCHES......................................................230
9.0 CONNECTOR PINOUTS................................................231
A/C COMPRESSOR CLUTCH - LT. GRAY 2 WAY............................231
A/C PRESSURE SENSOR - GRAY 4 WAY..................................231
ACCELERATOR PEDAL POSITION SENSOR (DIESEL) - BLACK 10 WAY........231
BATTERY TEMPERATURE SENSOR (DIESEL) - BLACK 2 WAY................231
BOOST PRESSURE SENSOR (DIESEL) - BLACK 4 WAY.....................232
BRAKE LAMP SWITCH - BLACK 6 WAY...................................232
CAMSHAFT POSITION SENSOR (DIESEL) - BLACK 3 WAY...................232
CLUTCH PEDAL UPSTOP SWITCH (DIESEL) - RED 2 WAY...................232
CRANKSHAFT POSITION SENSOR (DIESEL) - BLACK 3 WAY................232
DATA LINK CONNECTOR - BLACK 16 WAY................................233
EGR SOLENOID (DIESEL) - LT. GRAY 2 WAY...............................233
ENGINE CONTROL MODULE C1 (DIESEL) - BLACK 81 WAY..................234
ENGINE CONTROL MODULE C1 (DIESEL) - BLACK 81 WAY..................235
ENGINE CONTROL MODULE C2 (DIESEL) - BLACK 40 WAY..................236
ENGINE COOLANT TEMP SENSOR (DIESEL) - BLUE 2 WAY.................236
ENGINE OIL PRESSURE SENSOR (DIESEL) - BLACK 3 WAY.................237
ENGINE OIL TEMPERATURE SENSOR (DIESEL) - BLACK 2 WAY.............237
FUEL HEATER (DIESEL) - BLACK 2 WAY..................................237
FUEL INJECTOR NO. 1 (DIESEL) - BLACK 2 WAY...........................237
FUEL INJECTOR NO. 2 (DIESEL) - BLACK 2 WAY...........................237
FUEL INJECTOR NO. 3 (DIESEL) - BLACK 2 WAY...........................238
FUEL INJECTOR NO. 4 (DIESEL) - BLACK 2 WAY...........................238
FUEL PRESSURE SENSOR (DIESEL) - BLACK 3 WAY.......................238
FUEL PRESSURE SOLENOID (DIESEL) - BLACK 2 WAY.....................238
GENERATOR - BLACK 2 WAY...........................................238
GLOW PLUG RELAY (DIESEL) - BLACK 4 WAY.............................239
INTELLIGENT POWER MODULE C3 (DIESEL) - YELLOW/RED 20 WAY.........239
LEFT SPEED CONTROL SWITCH - WHITE 2 WAY..........................239
LIFT PUMP MOTOR (DIESEL) - BLACK 2 WAY..............................239
MASS AIR FLOW SENSOR (DIESEL) - ORANGE 5 WAY......................240
v

3.2.2 ECM OPERATING MODES
As input signals to the ECM change, the ECM
adjusts its response to the output devices. For
example, the ECM must calculate a different fuel
quantity and fuel timing for engine idle condition
than it would for a wide open throttle condition.
There are several different modes of operation that
determine how the ECM responds to the various
input signals.
Ignition Switch On (Engine Off)
When the ignition switch is turned on, the ECM
activates the glow plug relay for a time period that
is determined by engine coolant temperature, atmo-
spheric temperature and battery voltage. The ECM
also activates the lift pump to prime the fuel sys-
tem.
Engine Start-up Mode
The ECM uses the engine temperature sensor
and the crankshaft position sensor (engine speed)
inputs to determine fuel injection quantity.
Normal Driving Modes
Engine idle, warm-up, acceleration, deceleration
and wide open throttle modes are controlled based
on all of the sensor inputs to the ECM. The ECM
uses these sensor inputs to adjust fuel quantity and
fuel injector timing.
Overheat Protection Mode
If engine temperature is above 106É C (223É F)
and vehicle speed is above 40 km/h (25 MPH) the
ECM will activate the high speed fan and will limit
fuel quantity for engine protection.
Limp-In Mode
If there is a fault detected with the accelerator
pedal position sensor, the ECM will set the engine
speed at 1100 RPM.
Overspeed Detection Mode
If the ECM detects engine RPM that exceeds
5000 RPM, the ECM will set a DTC in memory and
limit engine RPM to no more that 2500 RPM until
the DTC(s) is cleared.
After-Run Mode
The ECM transfers RAM information to ROM
and performs an Input/Output state check.
3.2.3 MONITORED CIRCUITS
The ECM is able to monitor and identify most
driveability related trouble conditions. Some cir-
cuits are directly monitored through ECM feedback
circuitry. In addition, the ECM monitors the voltage
state of some circuits and compares those stateswith expected values. Other systems are monitored
indirectly when the ECM conducts a rationality test
to identify problems.
Although most subsystems of the engine control
module are either directly or indirectly monitored,
there may be occasions when diagnostic trouble
codes are not immediately identified. For a trouble
code to set, a specific set of conditions must occur
and unless these conditions occur, a DTC will not
set.
3.2.4 SKIS OVERIVEW
The sentry key immobilizer system (SKIS) is
designed to prevent unauthorized vehicle opera-
tion. The system consists of a sentry key immobi-
lizer module (SKIM), ignition key(s) equipped with
a transponder chip and the ECM. When the ignition
switch is turned on, the SKIM interrogates the
ignition key. If the ignition key is Valid or Invalid,
the SKIM sends a PCI Bus message to the ECM
indicating ignition key status. Upon receiving this
message the ECM will terminate engine operation
or allow the engine to continue to operate.
3.2.5 SKIS ON-BOARD DIAGNOSTICS
The sentry key immobilizer module (SKIM) has
been programmed to transmit and monitor many
different coded messages as well as PCI Bus mes-
sages. This monitoring is called On-Board Diagnos-
tics. Certain criteria must be met for a DTC to be
entered into SKIM memory. The criteria may be a
range of; input voltage, PCI Bus message or coded
messages to the SKIM. If all of the criteria for
monitoring a circuit or function are met and a fault
is detected, a DTC will be stored in the SKIM
memory.
3.2.6 SKIS OPERATION
When ignition power is supplied to the SKIM, the
SKIM performs an internal self-test. After the self-
test is complete, the SKIM energizes the antenna
(this activates the transponder chip) and sends a
challenge to the transponder chip. The transponder
chip responds to the challenge by generating an
encrypted response message using the following:
Secret Key - This is an electronically stored value
(identification number) that is unique to each SKIS.
The secret key is stored in the SKIM, ECM and all
ignition key transponders.
Challenge - This is a random number that is gen-
erated by the SKIM at each ignition key cycle.
The secret key and challenge are the two vari-
ables used in the algorithm that produces the
encrypted response message. The transponder uses
the crypto algorithm to receive, decode and respond
to the message sent by SKIM. After responding to
the coded message, the transponder sends a tran-
2
GENERAL INFORMATION