Backup Lamps Malfunction
Backup Lamps Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (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 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. The engine may need to be running for the backup lamps to function.
Reference Information
Schematic Reference
Exterior Lights Schematics (Exterior Lights Schematics)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Description and Operation
Exterior Lighting Systems Description and Operation (Exterior Lighting Systems)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
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 backup lamps should turn ON and OFF when changing between the commanded states.
Circuit/System Testing
1. Ignition OFF, disconnect the X1 harness connector at the body fuse block.
2. Test for less than 5 ohm between the ground circuit terminal E2 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 K8 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 appropriate backup lamp.
6. Test for less than 5 ohm 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 control circuit 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