Backup Lamps Malfunction (Automatic Transmission)
Backup Lamps Malfunction (Automatic Transmission)
Diagnostic Instructions
* Perform theDiagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* ReviewStrategy 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
When the transmission is placed in the REVERSE position, the transmission control module (TCM) sends a serial data message to the body control module (BCM). The message indicates that the gear selector is in the REVERSE position. The BCM applies voltage to the backup lamp relay control circuit energizing the backup lamp relay coil . With the relay coil energized, the switch contacts close allowing battery voltage to flow through the VEH BCK/UP fuse to the left and right backup lamps. The BCM also supplies voltage the to inside rearview mirror via the backup lamp relay control circuit for automatic day/night operation. Once the driver moves the gear selector out of the REVERSE position, a serial data message is sent by the TCM requesting the BCM to remove voltage from the backup lamp control circuit.
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 Testing
1. Ignition OFF, disconnect the X2 harness connector at the underhood fuse block.
2. Ignition OFF, exterior lamps OFF, test for less that 5.0 ohms between the ground circuit terminal N5 and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
3. Connect the X2 harness connector at the underhood fuse block. Disconnect the X5 harness connector at the underhood fuse block.
4. Connect a test lamp between the control circuit terminal H8 and ground.
5. 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.
6. Ignition OFF, connect the X5 harness connector at the underhood fuse block. Disconnect the harness connector at the inoperative backup lamp.
7. Ignition OFF, exterior lamps OFF, test for less than 5.0 ohms between the ground circuit terminal GRD and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
8. Connect a test lamp between the control circuit terminal MJR and ground.
9. 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 underhood fuse block.
• If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, replace the underhood fuse block.
• If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, replace the underhood fuse block.
10. If all circuits test normal, test or replace the inoperative backup lamp.
Repair Instructions
Perform theDiagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Backup Lamp Bulb Replacement (Chevrolet) (Backup Lamp Bulb Replacement (Chevrolet))Backup Lamp Bulb Replacement (GMC) (Backup Lamp Bulb Replacement (GMC))
* Underhood Electrical Center or Junction Block Replacement (Underhood Electrical Center or Junction Block Replacement)
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming