Backup Lamps Malfunction Automatic Transmission

When the transmission is placed in the REVERSE position, the transmission control module (TCM) sends a serial data message to the body control module (BCM). The message indicates that the gear selector is in the REVERSE position. The BCM applies voltage to the backup lamp relay control circuit energizing the backup lamp relay coil . With the relay coil energized, the switch contacts close allowing battery voltage to flow through the VEH BCK/UP fuse to the left and right backup lamps. The BCM also supplies voltage the to inside rearview mirror via the backup lamp relay control circuit for automatic day/night operation. Once the driver moves the gear selector out of the REVERSE position, a serial data message is sent by the TCM requesting the BCM to remove voltage from the backup lamp control circuit.

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 X2 harness connector at the underhood fuse block.
2. Ignition OFF, exterior lamps OFF, test for less that 5.0 ohms between the ground circuit terminal N5 and ground.

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

3. Connect the X2 harness connector at the underhood fuse block. Disconnect the X5 harness connector at the underhood fuse block.
4. Connect a test lamp between the control circuit terminal H8 and ground.
5. 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 voltage. If the circuit tests normal, replace the BCM.

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

6. Ignition OFF, connect the X5 harness connector at the underhood fuse block. Disconnect the harness connector at the inoperative backup lamp.
7. Ignition OFF, exterior lamps OFF, test for less than 5.0 ohms between the ground circuit terminal GRD and ground.

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

8. Connect a test lamp between the control circuit terminal MJR and ground.
9. 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 voltage. If the circuit tests normal, replace the underhood fuse block.

⇒	If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

⇒	If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, replace the underhood fuse block.

10. If all circuits test normal, test or replace the inoperative backup lamp.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Backup Lamps Malfunction Manual Transmission

When the transmission is placed in the REVERSE position, the backup lamp switch contacts close supplying ground to the engine control module (ECM) via the backup lamp switch signal circuit. The ECM responds by sending a serial data message to the body control module (BCM) indicating the gear selector is in the REVERSE position. The BCM applies voltage to the backup lamp relay control circuit energizing the backup lamp relay coil . With the relay coil energized, the switch contacts close allowing battery voltage to flow through the VEH BCK/UP fuse to the left and right backup lamps. The BCM also supplies voltage the to inside rearview mirror via the backup lamp relay control circuit for automatic day/night operation. Once the driver moves the gear selector out of the REVERSE position, the backup lamp switch contacts open and a serial data message is sent by the ECM requesting the BCM to remove voltage from the backup lamp relay control circuit.

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

Ignition ON, 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.

Backup Lamp Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the backup lamp switch.
2. Ignition OFF, exterior lamps OFF, test for less that 5.0 ohms between the ground circuit terminal A and ground.

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

3. Ignition ON, verify the backup lamps are not illuminated.

⇒	If the backup lamps are illuminated, test the signal circuit terminal B for a short to ground. If the circuit tests normal, replace the ECM.

4. Install a 3A fused jumper wire between the signal circuit terminal B and ground. Verify the backup lamps are illuminated.

⇒	If the backup lamps do not illuminate, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

5. If all circuits test normal, test or replace the backup lamp switch.

Backup Lamps Malfunction

1. Ignition OFF, disconnect the X2 harness connector at the underhood fuse block.
2. Ignition OFF, exterior lamps OFF, test for less that 5.0 ohms between the ground circuit terminal N5 and ground.

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

3. Connect the X2 harness connector at the underhood fuse block. Disconnect the X5 harness connector at the underhood fuse block.
4. Connect a test lamp between the control circuit terminal H8 and ground.
5. 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 voltage. If the circuit tests normal, replace the BCM.

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

6. Ignition OFF, connect the X5 harness connector at the underhood fuse block. Disconnect the harness connector at the inoperative backup lamp.
7. Ignition OFF, exterior lamps OFF, test for less than 5.0 ohms between the ground circuit terminal GRD and ground.

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

8. Connect a test lamp between the control circuit terminal MJR and ground.
9. 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 voltage. If the circuit tests normal, replace the underhood fuse block.

⇒	If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

⇒	If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, replace the underhood fuse block.

10. If all circuits test normal, test or replace the inoperative backup lamp.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.