When the PRNDL is placed in the REVERSE position, a GMLAN signal is sent from the transmission control module (TCM) to the body control module (BCM). The BCM then applies voltage through the backup lamps voltage supply circuit to the back up lamps.

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

Scan Tool Reference

Ignition ON, place the PRNDL in the REVERSE position. The backup lamps should illuminate.

1. Ignition OFF, disconnect the harness connector at the appropriate tail lamp assembly.
2. Test for less than 1.0 ohm of resistance between the ground circuit terminal B and ground.

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

3. Connect a test lamp between the voltage supply circuit terminal A and the ground circuit terminal B.
4. Ignition ON, place the PRNDL in the reverse position. The test lamp should turn ON and OFF when changing between park and reverse.

⇒	If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the body control module.

⇒	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 body control module.

5. If all circuits test normal, test or replace the appropriate component.

Important: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.