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

Battery voltage is applied at all times to the backup lamp PCB relay which is an internal part of the body fuse block. 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 to the backup lamp relay control circuit energizing the relay. With the relay energized, battery voltage is applied through the switch side of the relay, the BCK/UP fuse, and the backup lamp supply voltage circuit to the left and right backup lamps.

Circuit/System Verification

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

Circuit/System Testing

1. Ignition ON, place the PRNDL in the REVERSE position.
2. With a test lamp connected to ground, probe each of the test points on the appropriate BCK/UP Fuse. The test lamp should illuminate at one or both of the fuse test points.

• If the test lamp does not illuminate at either test point or remains illuminated at all times with the PRNDL out of the REVERSE position, refer to the Backup Lamp PCB Relay Test.
• If the test lamp illuminates, refer to the Backup Lamp Circuit Test.

Backup Lamp PCB Relay Test

1. Ignition OFF, disconnect the X7 harness connector at the body fuse block.
2. Connect a test lamp between the control circuit terminal 57 and ground.
3. 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 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.

4. If the circuit tests normal, replace the body fuse block.

Backup Lamp Circuit Test

1. Ignition OFF, disconnect the harness connector at the inoperative backup lamp.
2. Ignition OFF, test for less than 5.0 ohms of resistance between the ground circuit terminal G and ground.

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

3. Connect a test lamp between the supply voltage 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 supply voltage circuit for a short to voltage. If the circuit tests normal, replace the body fuse block
• If the test lamp is always OFF, test the supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the body fuse block.

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
* Backup Lamp Replacement
* Body Wiring Harness Junction Block Replacement