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Symptom:
P1605-IGNITION SWITCH PLAUSIBILITY
When Monitored and Set Condition:
P1605-IGNITION SWITCH PLAUSIBILITY
When Monitored: With the ignition on.
Set Condition: The ECM detects a short to voltage on the Ignition Switch Sense circuit.
POSSIBLE CAUSES
INTERMITTENT CONDITION
ECM/PCM RELAY
ENGINE CONTROL MODULE
IGNITION SWITCH SENSE CIRCUIT SHORTED TO VOLTAGE
ECM/PCM RELAY OUTPUT CIRCUIT SHORTED TO VOLTAGE
ECM/PCM RELAY CONTROL CIRCUIT SHORTED TO GROUND
TEST ACTION APPLICABILITY
1 Turn the ignition on.
With the DRB, erase ECM DTCs.
Cycle the ignition switch on and off several times, pausing for at least 10 seconds at
each key off and key on.
Turn the ignition on.
With the DRB, read ECM DTCs.
Did this DTC reset?All
Ye s®Go To 2
No®Go To 6
2 Turn the ignition off.
Disconnect the ECM harness connectors.
Measure the voltage of all cavities in the ECM harness connectors.
Is the voltage above 2.0 volts on any of the cavities?All
Ye s®Go To 3
No®Replace and program the Engine Control Module in accordance
with the Service Information.
Perform ROAD TEST VERIFICATION - VER-2.
3 Turn the ignition off.
Disconnect the ECM harness connectors.
Measure the voltage on ECM harness connector C1, cavity 22.
Is voltage present on ECM harness connector C1, cavity 22?All
Ye s®Go To 4
No®Repair the Ignition Switch Sense circuit that measured above 2.0
volts for a short to voltage.
Perform ROAD TEST VERIFICATION - VER-2.
166
DRIVEABILITY - DIESEL
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TEST ACTION APPLICABILITY
4 Turn the ignition off.
Disconnect the ECM harness connectors.
Remove the ECM/PCM Relay from the IPM.
Turn the ignition on.
Measure the voltage on ECM harness connector C1 cavities 4 and 5.
Is the voltage below 2.0 volts on both circuits?All
Ye s®Go To 5
No®Repair the ECM/PCM Relay Output circuit for a short to voltage.
Perform ROAD TEST VERIFICATION - VER-2.
5 Turn the ignition off.
Disconnect the ECM harness connectors.
Remove the ECM/PCM Relay from the IPM.
Measure the resistance between ground and the ECM/PCM Relay Control circuit.
Is the resistance above 100k ohms?All
Ye s®Replace the ECM/PCM Relay.
Perform ROAD TEST VERIFICATION - VER-2.
No®Repair the ECM/PCM Relay Control circuit for a short to ground.
Perform ROAD TEST VERIFICATION - VER-2.
6WARNING: WHEN THE ENGINE IS OPERATING, DO NOT STAND IN A
DIRECT LINE WITH THE FAN. DO NOT PUT YOUR HANDS NEAR THE
PULLEYS, BELTS OR FAN. DO NOT WEAR LOOSE CLOTHING.
NOTE: The conditions that set the DTC are not present at this time. The
following list may help in identifying the intermittent condition.
With the engine running at normal operating temperature, monitor the DRB
parameters related to the DTC while wiggling the wiring harness. Look for param-
eter values to change and/or a DTC to set.
Review the DTC When Monitored and Set Conditions. If possible, try to duplicate the
conditions under which the DTC was set.
Refer to any Technical Service Bulletins (TSB) that may apply.
Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or
partially broken wires.
Visually inspect the related wiring harness connectors. Look for broken, bent, pushed
out, or corroded terminals.
Were any of the above conditions present?All
Ye s®Repair as necessary.
Perform ROAD TEST VERIFICATION - VER-2.
No®Test Complete.
167
DRIVEABILITY - DIESEL
P1605-IGNITION SWITCH PLAUSIBILITY ÐContinued
Page 1387 of 4284

Symptom List:
P1685-SKIM SYSTEM INVALID KEY CODE RECEIVED
P1685-SKIM SYSTEM INVALID SECRET KEY IN EEPROM
P1685-SKIM SYSTEM KEY COMMUNICATION TIMED OUT
P1685-SKIM SYSTEM SKIM ERROR
P1685-SKIM SYSTEM WRITE ACCESS TO EEPROM FAILURE
Test Note: All symptoms listed above are diagnosed using the same tests.
The title for the tests will be P1685-SKIM SYSTEM INVALID
KEY CODE RECEIVED.
When Monitored and Set Condition:
P1685-SKIM SYSTEM SKIM ERROR
When Monitored: With the ignition on and the immobilizer disarmed.
Set Condition: The ECM detects an open, short to ground, or short to voltage on the
immobilizer signal circuit.
P1685-SKIM SYSTEM WRITE ACCESS TO EEPROM FAILURE
When Monitored: With the ignition on.
Set Condition: The ECM determines that the coded message from the PCM does not
match the message programmed into memory.
POSSIBLE CAUSES
SKIM
INTERMITTENT CONDITION
CHECK FOR SKIM COMMUNICATION AND DTCS
TEST ACTION APPLICABILITY
1 Turn the ignition on.
With the DRB, check for Sentry Key Immobilizer Module communication and DTCs.
Are any SKIS problems or DTCs present?All
Ye s®Refer to symptom list for problems related to SKIM Communica-
tion and DTCs before continuing.
Perform ROAD TEST VERIFICATION - VER-2.
No®Go To 2
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DRIVEABILITY - DIESEL
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TEST ACTION APPLICABILITY
2 Turn the ignition on.
With the DRBIIIt, erase ECM DTCs.
Turn the ignition on and off several times pausing 10 seconds between each key cycle.
With the DRBIIIt, read the ECM DTCs.
Are any P1685 DTCs present?All
Ye s®Go To 3
No®Go To 4
3 Replace and program the SKIM in accordance with the Service Information.
Turn the ignition on.
With the DRBIIIt, erase ECM DTCs.
Turn the ignition on and off several times pausing for 10 seconds between key cycles.
With the DRBIIIt, read ECM DTCs.
Are there any P1685 DTC's present?All
Ye s®Replace and program the ECM in accordance with the Service
Information.
Perform ROAD TEST VERIFICATION - VER-2.
No®Test Complete.
4WARNING: WHEN THE ENGINE IS OPERATING, DO NOT STAND IN A
DIRECT LINE WITH THE FAN. DO NOT PUT YOUR HANDS NEAR THE
PULLEYS, BELTS OR FAN. DO NOT WEAR LOOSE CLOTHING.
NOTE: The conditions that set the DTC are not present at this time. The
following list may help in identifying the intermittent condition.
With the engine running at normal operating temperature, monitor the DRB
parameters related to the DTC while wiggling the wiring harness. Look for param-
eter values to change and/or a DTC to set.
Review the DTC When Monitored and Set Conditions. If possible, try to duplicate the
conditions under which the DTC was set.
Refer to any Technical Service Bulletins (TSB) that may apply.
Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or
partially broken wires.
Visually inspect the related wiring harness connectors. Look for broken, bent, pushed
out, or corroded terminals.
Were any of the above conditions present?All
Ye s®Repair as necessary.
Perform ROAD TEST VERIFICATION - VER-2.
No®Test Complete.
169
DRIVEABILITY - DIESEL
P1685-SKIM SYSTEM INVALID KEY CODE RECEIVED ÐContinued
Page 1389 of 4284

Symptom List:
P2120-ACC PEDAL POSITION SENSOR 1 CKT PLAUSIBILITY
P2120-ACC PEDAL POSITION SENSOR 1 CKT PLAUSIBILITY
WITH BRAKE SWITCH
P2120-ACC PEDAL POSITION SENSOR 1 CKT PLAUSIBILITY
WITH POTENTIOMETER
P2120-ACC PEDAL POSITION SENSOR 1 CKT SIGNAL VOLTAGE
TOO HIGH
P2120-ACC PEDAL POSITION SENSOR 1 CKT SIGNAL VOLTAGE
TOO LOW
P2120-ACC PEDAL POSITION SENSOR 1 CKT SUPPLY VOLTAGE
TOO HIGH OR LOW
Test Note: All symptoms listed above are diagnosed using the same tests.
The title for the tests will be P2120-ACC PEDAL POSITION
SENSOR 1 CKT PLAUSIBILITY.
When Monitored and Set Condition:
P2120-ACC PEDAL POSITION SENSOR 1 CKT PLAUSIBILITY
When Monitored: With the ignition on.
Set Condition: The Accelerator Pedal Position Sensor Signal is below 2% or above 21%
and the idle switch is not in the correct state. NOTE: The idle switch is designed to
transition when the accel position is approximately 16% (1.00 volt). This code sets the ECM
to Limp-in Mode, which includes a fixed engine speed of 1100 RPM.
P2120-ACC PEDAL POSITION SENSOR 1 CKT PLAUSIBILITY WITH BRAKE
SWITCH
When Monitored: With the ignition on.
Set Condition: The ECM detects the Accelerator Pedal and the Brake Pedal have been
depressed at the same time for longer than the allowable time.
P2120-ACC PEDAL POSITION SENSOR 1 CKT PLAUSIBILITY WITH POTENTI-
OMETER
When Monitored: With the ignition on.
Set Condition: The Accelerator Pedal Position Sensor Signal is below 0.20 volts, the idle
switch transitions at too high a percentage intermittently or the idle switch is not in the
correct state intermittently. NOTE: The idle switch is designed to transition when the accel
position is approximately 16% (1.00 volt). This code sets the ECM to Limp-in Mode, which
includes a fixed engine speed of 1100 RPM.
170
DRIVEABILITY - DIESEL
Page 1390 of 4284

P2120-ACC PEDAL POSITION SENSOR 1 CKT SIGNAL VOLTAGE TOO HIGH
When Monitored: With the ignition on.
Set Condition: The ECM detects voltage on the Accelerator Pedal Position Sensor Signal
circuit above 4.5 volts.
P2120-ACC PEDAL POSITION SENSOR 1 CKT SIGNAL VOLTAGE TOO LOW
When Monitored: With the ignition on.
Set Condition: The ECM detects voltage on the Accelerator Pedal Position Sensor Signal
circuit 0.0 volt.
P2120-ACC PEDAL POSITION SENSOR 1 CKT SUPPLY VOLTAGE TOO HIGH OR
LOW
When Monitored: With the ignition on.
Set Condition: The Accelerator Pedal Position Sensor 5-Volt Supply voltage is too high or
too low.
POSSIBLE CAUSES
APP SENSOR IDLE VOLTAGE
APP SENSOR WIDE OPEN THROTTLE VOLTAGE
ECM - 5-VOLT SUPPLY CIRCUIT
LOW IDLE POSITION SWITCH SENSE CIRCUIT SHORTED TO GROUND
SENSOR GROUND OPEN (APP SENSOR)
SENSOR GROUND OPEN (IDLE SWITCH)
INTERMITTENT CONDITION
5-VOLT SUPPLY CIRCUIT OPEN
APP SENSOR SIGNAL CIRCUIT OPEN
LOW IDLE POSITION SWITCH SENSE CIRCUIT OPEN
5-VOLT SUPPLY CIRCUIT SHORTED TO THE SENSOR GROUND CIRCUIT
VERIFY LOW IDLE POSITION SWITCH OPERATION
APP SENSOR SIGNAL CIRCUIT SHORTED TO GROUND
5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
VERIFY APP SENSOR OPERATION
APP SENSOR SIGNAL CIRCUIT SHORTED TO THE SENSOR GROUND CIRCUIT
LOW IDLE POSITION SWITCH SENSE CIRCUIT SHORTED TO THE SENSOR GROUND CIR-
CUIT
5-VOLT SUPPLY CIRCUIT SHORTED TO VOLTAGE
ECM - SENSOR GROUND OPEN
APP SENSOR CIRCUIT SHORTED TO VOLTAGE
171
DRIVEABILITY - DIESEL
P2120-ACC PEDAL POSITION SENSOR 1 CKT PLAUSIBILITY ÐContinued
Page 1391 of 4284

POSSIBLE CAUSES
APP SENSOR GROUND CIRCUIT SHORTED TO VOLTAGE
LOW IDLE POSITION SWITCH SENSE CIRCUIT SHORTED TO VOLTAGE
LOW IDLE POSITION SWITCH SENSE GROUND CIRCUIT SHORTED TO VOLTAGE
VERIFY CORRECT SWITCHING
ECM - APP SENSOR SIGNAL CIRCUIT
TEST ACTION APPLICABILITY
1NOTE: The brake switch must be operational for the result of this test to be
valid.
Turn the ignition off.
Disconnect the APP Sensor harness connector.
Connect one end of a jumper wire to the Low Idle Position Sense circuit at the APP
Sensor harness connector.
Turn the ignition on.
With the DRB III, monitor the Low Idle Position Switch input while tapping the other
end of the jumper wire to the Sensor Ground circuit at the APP Sensor harness
connector.
Does the DRB III change between IDLE and ABOVE IDLE when tapping the jumper
wire?All
Ye s®Go To 2
No®Go To 20
2 Turn the ignition on.
With the DRB III observe the Low Idle Position Switch input.
Press and release the accelerator pedal several times while observing the DRB III
display.
NOTE: The Low Idle Position Switch input should change from IDLE to
ABOVE IDLE when pressing and releasing the accelerator pedal.
Did Low Idle Position Switch input change between IDLE and ABOVE IDLE?All
Ye s®Go To 3
No®Replace the Accelerator Pedal Position Sensor in accordance with
the Service Information.
Perform ROAD TEST VERIFICATION - VER-2.
3NOTE: If DTC P0641 or P0651 is present with this DTC, diagnose DTCs
P0641 and P0651 before diagnosing this DTC.
Turn the ignition off.
Disconnect the APP Sensor harness connector.
Turn the ignition on.
Measure the voltage of the 5-volt Supply circuit in APP Sensor harness connector.
Is the voltage between 4.7 and 5.3 volts?All
Ye s®Go To 4
No®Go To 16
172
DRIVEABILITY - DIESEL
P2120-ACC PEDAL POSITION SENSOR 1 CKT PLAUSIBILITY ÐContinued
Page 1392 of 4284

TEST ACTION APPLICABILITY
4 Turn the ignition off.
Disconnect the APP Sensor harness connector.
Connect a jumper wire between APP Sensor Signal circuit and the 5-volt supply
circuit at the APP Sensor harness connector .
With the DRBIII, read the PEDAL OUTPUT VOLTS.
Does the DRBIII display between 4.0 and 5.5 volts?All
Ye s®Go To 5
No®Go To 12
5 Turn the ignition off.
Disconnect the APP Sensor harness connector.
Disconnect the ECM harness connectors.
Remove the ECM/PCM Relay from the PDC.
Connect a jumper wire between cavity 30 and cavity 87 ECM/PCM Relay connector.
Turn the ignition on.
Measure the voltage of the APP Sensor Ground circuit.
Is the voltage above 1.0 volt?All
Ye s®Repair the App Sensor Ground circuit for a short to voltage.
Perform ROAD TEST VERIFICATION - VER-2.
No®Go To 6
6 Turn the ignition off.
Disconnect the APP Sensor harness connector.
Disconnect the ECM harness connectors.
Measure the resistance of the Sensor Ground circuit between the APP Sensor and the
ECM.
Is the resistance below 10.0 ohms?All
Ye s®Go To 7
No®Repair the APP Sensor Ground circuit for an open.
Perform ROAD TEST VERIFICATION - VER-2.
7 Turn the ignition on.
With the DRB III, read the PEDAL OUTPUT VOLTS with the accelerator pedal in
the at rest position.
Does the DRB III display between 0.28 and 0.38 volt?All
Ye s®Go To 8
No®Replace the Accelerator Pedal Position Sensor in accordance with
the Service Information.
Perform ROAD TEST VERIFICATION - VER-2.
8 Turn the ignition on.
Fully depress the accelerator pedal.
With the DRBIII, read the PEDAL OUTPUT VOLTS.
Does the DRB III display between 4.1 and 4.6 volts?All
Ye s®Go To 9
No®Replace the Accelerator Pedal Position Sensor in accordance with
the Service Information.
Perform ROAD TEST VERIFICATION - VER-2.
173
DRIVEABILITY - DIESEL
P2120-ACC PEDAL POSITION SENSOR 1 CKT PLAUSIBILITY ÐContinued