Backup Lamps Malfunction Automatic Transmission

The underhood fuse block supplies battery voltage through the STOP/B/U/ LPS fuse to the coil and switch terminals of the BCK/UP LAMP Relay located in the body control module (BCM). When the transmission is placed in the REVERSE position, the transmission control module (TCM) sends a class 2 message to the BCM. The message indicates that the gear selector is in the REVERSE position. The BCM grounds the back up lamp relay control circuit of the reverse lamp relay . This energizes the reverse lamp relay, closing the switch side contacts and provides battery voltage to the REVERSE LAMPS fuse through to the backup lamps. The backup lamps are permanently grounded at G302. With both power and ground the backup lamps illuminate. Once the driver moves the gear selector out of the REVERSE position, a message is sent by the TCM via class 2 serial data requesting the BCM to remove ground from the back up lamp relay control circuit. This opens the REVERSE LAMP Relay switch contacts turning OFF the backup lamps.

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

Scan Tool Reference

1. Ignition OFF, disconnect the backup lamp relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay controlled output circuit and ground.

⇒	If the test lamp illuminates, test the relay controlled output circuit for a short to voltage.

3. Verify that a test lamp illuminates between the relay coil B+ circuit and ground.

⇒

If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the reverse lamp relay.

4. Verify that a test lamp illuminates between the relay switch B+ circuit and ground.

⇒	If the test lamp does not illuminate, test the relay switch B+ circuit for an open/high resistance.

5. Disconnect the harness connector at the inoperative backup lamp.
6. Test for less than 1.0 ohm of resistance between the inoperative backup lamp ground circuit terminal 1 and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the inoperative backup lamp.
8. Connect a 10A fused jumper wire between the relay switch B+ circuit and the relay controlled output circuit. Verify the backup lamps are activated.

⇒	If the backup lamps do not activate, test the relay controlled output circuit for an open/high resistance. If the circuit tests normal, test or replace the inoperative backup lamp.

9. Connect a test lamp between the relay coil B+ circuit and the relay coil control circuit.
10. Command the backup lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

11. If all circuits test normal, test or replace the reverse lamp relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Backup Lamps Malfunction Manual Transmission

The underhood fuse block supplies battery voltage through the STOP/B/U/ LPS fuse to the coil and switch terminals of the BCK/UP LAMP Relay located in the body control module (BCM). The BCM provides the normally open reverse switch with voltage. When the transmission is placed in the reverse position, the reverse switch closes providing a ground path through the reverse lamp relay control circuit to the BCM. The BCM then grounds the back up lamp relay control circuit of the reverse lamp relay . This energizes the reverse lamp relay, closing the switch side contacts and provides battery voltage to the REVERSE LAMPS fuse through to the backup lamps. The backup lamps are permanently grounded at G302. Once the driver moves the gear selector out of the REVERSE position, the reverse switch opens and the BCM removes ground from the back up lamp relay control circuit. This opens the REVERSE LAMP Relay switch contacts turning OFF the backup lamps.

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

Scan Tool Reference

1. Ignition OFF, disconnect the backup lamp relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay controlled output circuit and ground.

⇒	If the test lamp illuminates, test the relay controlled output circuit for a short to voltage.

3. Verify that a test lamp illuminates between the relay coil B+ circuit and ground.

⇒

If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the reverse lamp relay.

4. Verify that a test lamp illuminates between the relay switch B+ circuit and ground.

⇒	If the test lamp does not illuminate, test the relay switch B+ circuit for an open/high resistance.

5. Disconnect the harness connector at the inoperative backup lamp.
6. Test for less than 1.0 ohm of resistance between the inoperative backup lamp ground circuit terminal 1 and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the inoperative backup lamp.
8. Connect a 10A fused jumper wire between the relay switch B+ circuit and the relay controlled output circuit. Verify the backup lamps are activated.

⇒	If the backup lamps do not activate, test the relay controlled output circuit for an open/high resistance. If the circuit tests normal, test or replace the inoperative backup lamp.

9. Connect a test lamp between the relay coil B+ circuit and the relay coil control circuit.
10. Command the backup lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

11. Connect the reverse lamp relay.
12. Command the backup lamps ON and OFF with a scan tool. The backup lamps should turn ON and OFF when changing between the commanded states.

⇒	If the backup lamps do not activate, replace the reverse lamp relay.

13. Ignition OFF, disconnect the harness connector at the reverse lamp switch.
14. Test for less than 1.0 ohm of resistance between the control circuit terminal 1 and ground.

⇒	If greater than the specified range, test the control circuit for a short to voltage or an open/high resistance. If circuits test normal, replace the BCM.

15. Ignition OFF, disconnect the C2 harness connector at the BCM.
16. Verify a test lamp does not illuminate between B+ and the relay control circuit terminal 1.

⇒	If the test lamp illuminates, test the relay control circuit for a short to ground.

17. Reconnect the C2 harness connector at the BCM.
18. Ignition ON, verify a test lamp illuminates between the supply voltage circuit terminal 2 and ground.

⇒	If the test lamp does not illuminate, test the voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

19. If all circuits test normal, test or replace the reverse lamp switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.