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 serial data 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 backup lamp relay. This energizes the backup 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 serial data requesting the BCM to remove ground from the back up lamp relay control circuit. This opens the backup lamp relay switch contacts turning OFF the backup lamps.

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, disconnect the backup lamp relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

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

3. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.

⇒	If the test lamp does not illuminate, test the 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 control circuit terminal 87 for a short to ground. If the circuit tests normal, test or replace the backup lamp relay.

4. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.

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

5. Disconnect the harness connector at the inoperative backup lamp.
6. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the 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 B+ circuit terminal 30 and the control circuit terminal 87. Verify the backup lamps illuminate.

⇒	If the backup lamps do not illuminate, test the control 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 B+ circuit terminal 85 and the control circuit terminal 86.
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 control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the 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 backup 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 backup lamp relay. This energizes the backup 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 backup lamp relay control circuit. This opens the backup lamp relay switch contacts turning OFF the backup lamps.

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, disconnect the backup lamp relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

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

3. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.

⇒	If the test lamp does not illuminate, test the 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 control circuit terminal 87 for a short to ground. If the circuit tests normal, test or replace the backup lamp relay.

4. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.

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

5. Disconnect the harness connector at the inoperative backup lamp.
6. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the 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 B+ circuit terminal 30 and the control circuit terminal 87. Verify the backup lamps are illuminate.

⇒	If the backup lamps do not illuminate, test the control 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 B+ circuit terminal 85 and the control circuit terminal 86.
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 control circuit for a short to ground. If the circuit tests normal, replace the BCM.

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

11. Connect the backup 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 backup lamp relay.

13. Ignition OFF, disconnect the harness connector at the reverse lamp switch.
14. Ignition OFF, exterior lamps OFF, test for less than 5 ohms 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 X2 harness connector at the BCM.
16. Verify that a test lamp does not illuminate between B+ and the control circuit terminal 1 at the reverse lamp switch harness connector.

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

17. Reconnect the X2 harness connector at the BCM.
18. Ignition ON, verify that a test lamp illuminates between the control circuit terminal 2 and ground.

⇒	If the test lamp does not illuminate, test the control 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.