Symptom:
FCM, PCM COMMUNICATION FAULT
When Monitored and Set Condition:
FCM, PCM COMMUNICATION FAULT
When Monitored: With the ignition in run, and the IOD fuse installed.
Set Condition: The FCM does not receive any messages from the PCM for at least 5
seconds.
POSSIBLE CAUSES
PCM COMMUNICATION FAULT
ATTEMPT TO COMMUNICATE WITH THE PCM
PCI BUS CIRCUIT OPEN
POWERTRAIN CONTROL MODULE
TEST ACTION APPLICABILITY
1 Turn the ignition on.
With the DRB, enter Instrument Cluster, System Tests then PCM Monitor.
Does the DRB display: PCM is active on BUS?All
Ye s®Erase the DTC, if DTC resets, replace the Front Control Module.
Perform BODY VERIFICATION TEST - VER 1.
No®Go To 2
2 Turn the ignition on.
With the DRB, attempt to communicate with the PCM.
Was the DRB able to communicate with the PCM?All
Ye s®Go To 3
No®Refer to the communication category and perform the appropriate
symptom.
Perform BODY VERIFICATION TEST - VER 1.
3 Turn the ignition off.
Disconnect the PCM C2 harness connector.
Connect the diagnostic junction port tester #8339 to the diagnostic junction port.
Note: Do not connect the tester to the DRB.
Measure the resistance of the PCI Bus circuit between the diagnostic junction port
tester and the PCM C2 connector.
Is the resistance below 5.0 ohms?All
Ye s®Replace and program the Powertrain Control Module in accor-
dance with the Service Information.
Perform BODY VERIFICATION TEST - VER 1.
No®Repair the PCI Bus circuit for an open.
Perform BODY VERIFICATION TEST - VER 1.
347
COMMUNICATION
Symptom:
IGNITION MUX SWITCH INPUT OPEN
When Monitored and Set Condition:
IGNITION MUX SWITCH INPUT OPEN
When Monitored: With the ignition on and battery voltage greater than 10.4 volts.
Set Condition: The Ignition MUX sense circuit voltage at the BCM goes above 4.9 volts.
POSSIBLE CAUSES
IGNITION SWITCH
IGNITION SWITCH SENSE CIRCUIT OPEN
IGNITION SWITCH SENSE RETURN CIRCUIT OPEN
BODY CONTROL MODULE
BODY CONTROL MODULE
TEST ACTION APPLICABILITY
1 Turn the ignition off.
Disconnect the ignition switch 5-way connector.
Connect a jumper wire between the Ignition Switch Sense circuit and ground.
With the DRBIIItin Sensors, read the IGNITION SW voltage.
Does the DRBIIItdisplay IGNITION SW 0.0 volts?All
Ye s®Go To 2
No®Go To 3
2 Turn the ignition off.
Gain access to the Body Control Module C5 connector.
Backprobe a jumper wire between the Ignition Switch Sense circuit and ground.
With the DRBIIItin Sensors, read the IGNITION SW voltage.
Does the DRBIIItdisplay IGNITION SW 0.0 volts?All
Ye s®Repair the Ignition Switch Sense circuit for an open.
Perform BODY VERIFICATION TEST - VER 1.
No®Replace the Body Control Module.
Perform BODY VERIFICATION TEST - VER 1.
3 Turn the ignition off.
Disconnect the ignition switch connector.
Connect a jumper wire between the Ignition Switch Sense circuit and the Ignition
Switch Sense Return circuit.
With the DRBIIItin Sensors, read the IGNITION SW voltage.
Does the DRBIIItdisplay IGNITION SW 0.0 volts?All
Ye s®Replace the Ignition Switch.
Perform BODY VERIFICATION TEST - VER 1.
No®Go To 4
350
COMMUNICATION
TEST ACTION APPLICABILITY
4 Turn the ignition off.
Gain access to the Body Control Module C4 connector.
Backprobe a jumper wire between the Ignition Switch Sense Return circuit and
ground.
With the DRBIIItin Sensors, read the IGNITION SW voltage.
Does the DRBIIItdisplay IGNITION SW 0.0 volts?All
Ye s®Repair the Ignition Switch Sense Return circuit for an open.
Perform BODY VERIFICATION TEST - VER 1.
No®Replace the Body Control Module.
Perform BODY VERIFICATION TEST - VER 1.
351
COMMUNICATION
IGNITION MUX SWITCH INPUT OPEN ÐContinued
Symptom:
IGNITION MUX SWITCH INPUT SHORT
When Monitored and Set Condition:
IGNITION MUX SWITCH INPUT SHORT
When Monitored: With the ignition on and battery voltage greater than 10.4 volts.
Set Condition: The Ignition MUX Sense circuit voltage at the BCM goes below 0.5 volt for
more than 2 seconds.
POSSIBLE CAUSES
IGNITION SWITCH SENSE CIRCUIT SHORTED
IGNITION SWITCH SENSE RETURN CIRCUIT OPEN
IGNITION SWITCH SHORTED
BODY CONTROL MODULE
TEST ACTION APPLICABILITY
1 Turn the ignition off.
Disconnect the ignition switch 5-way connector.
With the DRBIIItin Sensors, read the IGNITION SW voltage.
Does the DRBIIItdisplay IGNITION SW 0.0 volts?All
Ye s®Go To 2
No®Replace the Ignition Switch.
Perform BODY VERIFICATION TEST - VER 1.
2 Turn the ignition off.
Gain access to the Body Control Module.
Disconnect the Body Control Module C5 connector.
Measure the resistance of the Ignition Switch Sense circuit in the BCM C5 connector.
Is the resistance below 5.0 ohms?All
Ye s®Repair the Ignition Switch Sense circuit for a short to ground.
Perform BODY VERIFICATION TEST - VER 1.
No®Go To 3
3 Turn the ignition off.
Gain access to the Body Control Module.
Disconnect the Body Control Module C4 connector.
Measure the resistance of the Ignition Switch Sense Return circuit in the BCM C4
connector.
Is the resistance below 5.0 ohms?All
Ye s®Repair the Ignition Switch Sense Return circuit for an open.
Perform BODY VERIFICATION TEST - VER 1.
No®Replace the Body Control Module.
Perform BODY VERIFICATION TEST - VER 1.
352
COMMUNICATION
Symptom:
IGNITION RUN OUTPUT SHORT
When Monitored and Set Condition:
IGNITION RUN OUTPUT SHORT
When Monitored: With the ignition on and battery voltage greater than 10.4 volts.
Set Condition: The Ignition Switch Output circuit(s) from the BCM to the HVAC,
Overhead Console, or the ABS controller are open or go below 0.5 volt for more than 2
seconds.
POSSIBLE CAUSES
TEST FOR CURRENT DTC'S
BODY CONTROL MODULE IGNITION OUTPUT INOPERATIVE (HVAC)
BODY CONTROL MODULE IGNITION OUTPUT CIRCUIT OPEN (HVAC)
BODY CONTROL MODULE IGNITION OUTPUT CIRCUIT SHORTED (HVAC)
BODY CONTROL MODULE IGNITION OUTPUT INOPERATIVE (OVERHEAD)
BODY CONTROL MODULE IGNITION OUTPUT CIRCUIT OPEN (OVERHEAD)
BODY CONTROL MODULE IGNITION OUTPUT CIRCUIT SHORTED (OVERHEAD)
BODY CONTROL MODULE IGNITION OUTPUT INOPERATIVE (ABS)
BODY CONTROL MODULE IGNITION OUTPUT CIRCUIT OPEN (ABS)
BODY CONTROL MODULE IGNITION OUTPUT CIRCUIT SHORTED (ABS)
BODY CONTROL MODULE
TEST ACTION APPLICABILITY
1 With the DRBIIIt, record and erase DTC's.
Cycle the ignition from ON to OFF.
Start the vehicle and observe the DRBIIIt.
With the DRBIIIt, read DTC's.
Does the DRBIIItdisplay IGNITION RUN OUTPUT SHORT?All
Ye s®Go To 2
No®The condition that caused this DTC is currently not present. Use
the wiring diagram/schematic as a guide, and inspect the related
wiring harness for a possible intermittent condition.
2 A failure in the HVAC, Overhead Console, or the ABS system could cause this DTC
to set. The Ignition Switch Run (HVAC) circuit will be diagnosed first.
Continue to the HVAC circuit for further diagnosis.All
HVAC circuit diagnostics.
Go To 3
353
COMMUNICATION
TEST ACTION APPLICABILITY
2 Use Scope input cable CH7058, Cable to Probe adapter CH7062, and the red and
black test probes.
Connect the scope input cable to the channel one connector on the DRB. Attach the
red and black leads and the cable to probe adapter to the scope input cable.
Select DRB Standalone.
Select lab scope.
Select Live.
Select 12 volt square wave.
Press F2 for Scope.
Press F2 and use the down arrow to set voltage range to 20 volts. Press F2 again
when complete.
Disconnect the CD Changer harness connector (DIN cable).
Reconnect the Radio C4 (DIN Cable) harness connector.
Connect the Black lead to the chassis ground. Connect the Red lead to the PCI Bus
circuit in the CD Changer DIN Cable connector.
Turn the ignition on.
Turn the Radio and CD Changer on.
Observe the voltage display on the DRB Lab Scope.
Does the voltage pulse from 0 to approximately 7.5 volts?All
Ye s®Go To 3
No®Replace the Radio.
Perform BODY VERIFICATION TEST - VER 1.
3 Turn the ignition off.
Disconnect the CD Changer harness connector (DIN cable).
Turn the ignition on.
Turn the Radio and the CD Changer on.
Using a 12-volt test light connected to ground, probe the Ignition Switch Output
circuit in the CD Changer DIN Cable connector.
Is the test light illuminated?All
Ye s®Go To 4
No®Replace the Radio.
Perform BODY VERIFICATION TEST - VER 1.
4 Turn the ignition off.
Disconnect the CD Changer harness connector (DIN cable).
Using a 12-volt test light connected to 12-volts, probe the CD Changer ground circuit
in the CD Changer connector (DIN cable).
Is the test light illuminated?All
Ye s®Go To 5
No®Replace the Radio.
Perform BODY VERIFICATION TEST - VER 1.
5 If there are no possible causes remaining, view repair. All
Repair
Replace the CD Changer.
Perform BODY VERIFICATION TEST - VER 1.
363
COMMUNICATION
NO PCI MESSAGES FROM CD CHANGER ÐContinued
Symptom:
PCM MESSAGES NOT RECEIVED
When Monitored and Set Condition:
PCM MESSAGES NOT RECEIVED
When Monitored: With the ignition in run, and the IOD fuse installed.
Set Condition: The BCM does not receive any messages from the PCM for at least 5
seconds.
POSSIBLE CAUSES
PCM MESSAGE NOT RECEIVED
ATTEMPT TO COMMUNICATE WITH THE PCM
PCI BUS CIRCUIT OPEN
POWERTRAIN CONTROL MODULE
TEST ACTION APPLICABILITY
1 Turn the ignition on.
With the DRB, enter Instrument Cluster, System Tests then PCM Monitor.
Does the DRB display: PCM is active on BUS?All
Ye s®Erase the DTC, if DTC resets, replace the Body Control Module.
Perform BODY VERIFICATION TEST - VER 1.
No®Go To 2
2 Turn the ignition on.
With the DRB, attempt to communicate with the PCM.
Was the DRB able to communicate with the PCM?All
Ye s®Go To 3
No®Refer to the communication category and perform the appropriate
symptom.
Perform BODY VERIFICATION TEST - VER 1.
3 Turn the ignition off.
Disconnect the PCM C2 harness connector.
Connect the diagnostic junction port tester #8339 to the diagnostic junction port.
Note: Do not connect the tester to the DRB.
Measure the resistance of the PCI Bus circuit between the diagnostic junction port
tester and the PCM C2 connector.
Is the resistance below 5.0 ohms?All
Ye s®Replace and program the Powertrain Control Module in accor-
dance with the Service Information.
Perform BODY VERIFICATION TEST - VER 1.
No®Repair the PCI Bus circuit for an open.
Perform BODY VERIFICATION TEST - VER 1.
367
COMMUNICATION
Symptom:
RUN/START HARDWIRE INPUT FAILURE
When Monitored and Set Condition:
RUN/START HARDWIRE INPUT FAILURE
When Monitored: With the ignition on and battery voltage greater than 10.4 volts.
Set Condition: The Fused Ignition Switch Output circuit voltage at the BCM goes below
0.5 volts and the BCM detects a voltage mismatch between the two ignition switch inputs.
POSSIBLE CAUSES
TEST FOR CURRENT DTC'S
FUSED IGNITION SWITCH OUTPUT CIRCUIT OPEN
IGNITION SWITCH
BODY CONTROL MODULE
TEST ACTION APPLICABILITY
1 With the DRBIIIt, record and erase DTC's.
Cycle the ignition from ON to OFF.
Start the vehicle and observe the DRBIIIt.
With the DRBIIIt, read DTC's.
Does the DRBIIItdisplay RUN/START HARDWIRE INPUT FAILURE?All
Ye s®Go To 2
No®The condition that caused this DTC is currently not present. Use
the wiring diagram/schematic as a guide, and inspect the related
wiring harness for a possible intermittent condition.
Perform BODY VERIFICATION TEST - VER 1.
2 Turn the ignition off.
Gain access to the Ignition Switch connector.
Turn the ignition on.
While back probing, measure the voltage of the Fused Ignition Switch Output circuit.
Is the voltage above 10.0 volts?All
Ye s®Go To 3
No®Replace the Ignition Switch.
Perform BODY VERIFICATION TEST - VER 1.
3 Turn the ignition off.
Gain access to the Body Control Module C2 connector.
While back probing, measure the voltage of the Fused Ignition Switch Output circuit.
Is the voltage above 10.0 volts?All
Ye s®Repair the Fused Ignition Switch Output circuit for an open.
Perform BODY VERIFICATION TEST - VER 1.
No®Replace the Body Control Module.
Perform BODY VERIFICATION TEST - VER 1.
370
COMMUNICATION