Backup Lamps Malfunction
Backup Lamps Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) 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 T/LAMP BCK/UP fuse, and the backup lamp supply voltage circuit to the left and right backup lamps. Or, the AUX/TRLR BCK/UP fuse and the supply voltage circuit to the backup alarm and the trailer connector.
Reference Information
Schematic Reference
Exterior Lights Schematics (Exterior Lights Schematics)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Exterior Lighting Systems Description and Operation (Exterior Lighting Systems Description and Operation)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
Ignition ON, 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.
Circuit/System Testing
Backup Lamps Malfunction
1. Ignition OFF, disconnect the X1 harness connector at the body fuse block.
2. Test for less than 5 ohms between the ground circuit terminal 22 and ground.
• If greater then the specified range, test the ground circuit for and open/high resistance.
3. Connect a test lamp between the control circuit terminal 57 and ground.
4. Ignition ON, 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. Ignition OFF, disconnect the inoperative backup lamp.
6. Test for less than 5 ohms between the ground circuit terminal G and ground.
• If greater than the specified range, test the ground circuit for a open/high resistance.
7. Connect a test lamp between the backup lamp control terminal A and ground.
8. Command the backup lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF between the commanded states.
• If the test lamp is always ON, test the control circuit for short to voltage.
• If the test lamp is always OFF, test the control circuit for a short to ground or and open/high resistance.
9. If the circuits test normal, replace the body fuse block.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Backup Lamp Bulb Replacement (Service and Repair)
* Backup Lamp Replacement (Service and Repair)
* Body Wiring Harness Junction Block Replacement (Body Wiring Harness Junction Block Replacement)
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming