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 Body Control Module (BCM) receives a class 2 message from the Powertrain Control Module (PCM) requesting to illuminate the backup lamps, battery voltage is sent directly from the BCM through the backup lamp supply voltage circuit to the backup lamps.

Circuit/System Verification

Ignition ON, shift the vehicle in and out of reverse. The backup lamps should turn on and off.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at an affected backup lamp.
2. Test for less than 1 ohm of resistance between the listed ground circuit terminal and ground.

* Chevy, Isuzu terminal E
* GMC terminal G

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

3. Connect a test lamp between the listed control circuit terminal and ground circuit terminal.

* Chevy, Isuzu terminal C
* GMC terminal A

4. 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.

5. If all circuits test normal, test or replace the affected backup lamps.

Repair Instructions

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

* Backup Lamp Replacement (GMC)