Backup Lamps Malfunction

Backup Lamps Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Fault Information






Circuit/System Description

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 battery voltage from the CHMSL/BCK-UP fuse through the backup lamps voltage supply circuit to the tail lamp assemblies illuminating the backup lamps.

Circuit/System Verification

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

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate tail lamp assembly.
2. Test for less than 10 ohms 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 control circuit terminal A and ground.
4. Ignition ON, cycle the PRNDL between the PARK and REVERSE positions. 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 backup lamp bulb.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Backup Lamp Bulb Replacement
* Tail Lamp Replacement (Impala)
* Inside Rearview Mirror Replacement.