When the transmission is placed in the REVERSE position, the transmission control module (TCM) sends a GMLAN serial data message to the body control module (BCM). The message indicates that the gear selector is in the REVERSE position. The BCM applies battery voltage to the backup lamp control circuit to the left rear fuse block. The left rear fuse block distributes the battery voltage to the backup lamps and inside rearview mirror. The backup lamps are permanently grounded at G402. Once the driver moves the gear selector out of the REVERSE position, a message is sent by the TCM via GMLAN serial data requesting the BCM to remove battery voltage from the backup lamp control circuit.

Battery voltage must be between 9-16 volts.

DTC B2545 00 will set when the BCM detects a short to ground or an open/high resistance in the backup lamps control circuit or the BCM 4 fuse voltage supply circuit.

When DTC B2545 00 is present, the backup lamps will not operate.

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 joint connector at the left rear fuse block.
2. Connect a test lamp between the backup lamp supply voltage circuit terminal S17 and ground.
3. 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, test the BCM 4 fuse voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

4. Disconnect the harness connector at the inside rearview mirror.
5. Verify that a test lamp does not illuminate between the inside rearview mirror backup lamp supply voltage circuit terminal 9 and B+.

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

6. Connect the harness connector at the inside rearview mirror.
7. Ignition ON, verify that a test lamp illuminates between the inside rearview mirror backup lamp supply voltage circuit terminal S15 and B+.

⇒	If the test lamp does not illuminate, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the inside rearview mirror.

8. Disconnect the harness connector at the inoperative backup lamp.
9. Ignition OFF, exterior lamps OFF, test for less than 5.0 ohms of resistance between the inoperative backup lamp ground circuit terminal B and ground.

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

10. Ignition ON, verify that a test lamp does not illuminate between the backup lamp supply voltage circuit terminal S16 and ground.

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

11. Connect the harness connector at the inoperative backup lamp.
12. Connect a 10-A fused jumper wire between the backup lamp supply voltage circuit terminal S16 and B+. Verify the backup lamps are activated.

⇒	If the backup lamps do not activate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the inoperative backup lamp.

13. If all circuits test normal, test or replace the left rear fuse block.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.