Troubleshooting

(Table 69, contd)
Troubleshooting Test Steps
Values Results
9. Check the GCU Wiring for an Open Circuit
A. Turn the keyswitch to the OFF position.
B. Disconnect the GCU.
C. Disconnect the P1 connector from the ECM.
D. Use a multimeter to measure the resistance between the
following points:
• Terminal 8 on the GCU harness connector and P1:52
• Terminal 5 on the GCU harness connector and P1:41
Less than 5
Ohms
Result: The measured resistance is not within the expected
range.
There is an open circuit or high resistance in the wiring be-
tween the GCU and the P1 connector.
Inspect the 9-pin engine interface connector (if equipped). Re-
pair the faulty wiring or replace the faulty wiring.
Result: The measured resistance is within the expected
range.
Proceed to Test Step 10.
10. Check the GCU Wiring for a Short to Ground
A. Turn the keyswitch to the OFF position.
B. Disconnect the GCU.
C. Disconnect the P1 connector from the ECM.
D. Use a multimeter to measure the resistance between the
following terminals and a suitable engine ground:
• Terminal 8 on the GCU harness connector
• Terminal 3 on the GCU harness connector
• Terminal 5 on the GCU harness connector
Greater than 1
k Ohm
Result: The measured resistance is not within the expected
range.
There is a short to ground in the wiring between the GCU and
the P1 connector.
Inspect the 9-pin engine interface connector (if equipped). Re-
pair the faulty wiring or replace the faulty wiring.
Result: The measured resistance is within the expected
range.
Repair: Install a replacement GCU.
Use the electronic service tool to override the glow plug start-
ing aid and verify that the repair eliminates the fault.
Clear all logged diagnostic codes.
If the repair does not eliminate the fault, contact the Dealer
Solutions Network (DSN).
11. Check the GCU Wiring for a Short Circuit
A. Turn the keyswitch to the OFF position.
B. Disconnect the GCU.
C. Disconnect the P1 connector from the ECM.
D. Use a multimeter to measure the resistance between the
following points:
• P1:52 and all other terminals on the P1 connector
• P1:22 and all other terminals on the P1 connector
• P1:41 and all other terminals on the P1 connector
Greater than 1
k Ohm
Result: At least one of the resistance measurements is not
within the expected range.
There is a short in the wiring between the GCU connector and
the P1 ECM connector.
Inspect the 9-pin engine interface connector (if equipped). Re-
pair the faulty wiring or replace the faulty wiring.
Result: All resistance measurements are within the expected
range.
Repair: Install a replacement GCU.
Use the electronic service tool to override the glow plug start-
ing aid and verify that the repair eliminates the fault.
Clear all logged diagnostic codes.
If the repair does not eliminate the fault, contact the Dealer
Solutions Network (DSN).
12. Check the Diagnostic Return Wire From the GCU
A. Turn the keyswitch to the OFF position.
B. Disconnect the GCU. Disconnect the P1/J1 connector.
C. Measure the resistance between pin 3 on the harness con-
nector for the GCU and P1:22.
Less than 5
Ohms
Result: The measured resistance is greater than 5 Ohms.
There is an open circuit or high resistance in the wiring.
Repair: Repair the faulty wiring or replace the faulty wiring.
Result: The measured resistance is less than 5 Ohms.
Contact the Dealer Solution Network (DSN).
UENR0612-07 139
Circuit Tests
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