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

When the engine is running and the transmission is placed in reverse gear, the transmission control module 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 battery voltage to the backup lamps. Once the driver moves the gear selector out of the reverse position, a message is sent by the transmission control module via serial data requesting the BCM to remove battery voltage from the backup lamp signal circuit. The BCM will not apply battery voltage to the backup lamps if the engine is not running.

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 Control Module References for scan tool information

Circuit/System Verification

Engine running, command the Backup Lamps ON and OFF with a scan tool. The E5A backup lamp-left and the E5B backup lamp-right should turn ON and OFF when changing between the commanded states.

If the E5A backup lamp-left or the E5B backup lamp-right is always OFF, inspect for a burned out bulb or corrosion of the bulb sockets.

If the E5A backup lamp-left and the E5B backup lamp-right are always OFF or always ON, perform the Circuit/System Testing.

Circuit/System Testing

1. Ignition OFF, disconnect the X2 harness connector K9 BCM.
2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 1 and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

3. Ignition OFF, connect the X2 harness connector K9 BCM
4. Disconnect the harness connector at the E5A backup lamp listed below:

* X3 harness connector E5E tail lamp-left (Without T79)
* X1 harness connector E5E tail lamp-left (With T79)
* X3 harness connector E5F tail lamp-right (Without T79)
* X1 harness connector E5F tail lamp-right (With T79)

5. Test for less than 30 ohm between the ground circuit terminal listed below and ground.

* E5E tail lamp-left (Without T79) ground terminal 2
* E5E tail lamp-left (With T79) ground terminal C
* E5F tail lamp-right (Without T79) ground terminal 2
* E5F tail lamp-right (With T79) ground terminal C

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

6. Connect a test lamp between the control circuit terminal listed below and ground:

* E5E tail lamp-left (Without T79) control terminal 1
* E5E tail lamp-left (With T79) control terminal D
* E5F tail lamp-right (Without T79) control terminal 1
* E5F tail lamp-right (With T79) control terminal D

7. Engine running, command the Backup Lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the selected states.

• If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K9 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 K9 BCM.

8. If all circuits test normal, test or replace the E5A backup lamp-left and the E5B backup lamp-right.

Repair Instructions

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

* Backup Lamp Bulb Replacement Service and Repair
* Control Module References Control Module References for BCM replacement, setup and programming