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

The BCK/UP fuse in the underhood fuse block supplies B+ to the normally open park/neutral position (PNP) switch used in a vehicle equipped with an automatic transmission or the backup lamp switch if equipped with a manual transmission. When the driver places the gear select lever in the REVERSE position, the switch closes and the current flows through the switch to the backup lamps. The backup lamps are grounded at G350 and G340.


Reference Information
Schematic Reference

Exterior Lights Schematics (Exterior Lights Schematics)
Connector End View Reference

Component Connector End Views (Component Connector End 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

1. Ignition ON, with the transmission in park or neutral the backup lamps should not illuminate.
2. Shift the transmission into reverse, the backup lamps should illuminate.



Circuit/System Testing

1. Ignition OFF, disconnect the park neutral position or backup lamp switch connector.
2. Ignition ON, the backup lamps should not be illuminated.

• If the backup lamps are illuminated, test the listed backup lamp control circuit for a short to voltage.


* Park neutral position switch terminal 10
* Backup lamp switch terminal B

3. Connect a test lamp between the listed switch control circuit and ground. The test lamp should illuminate.

* Park neutral position switch terminal 11
* Backup lamp switch terminal A


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

4. Connect a 15 amp fused jumper wire between the listed switch supply circuit and backup lamp control circuit. Both backup lamps should illuminate.

* Park neutral position switch terminal 11 and terminal 10
* Backup lamp switch terminal A and terminal B


• If both backup lamps are not illuminated, test the backup lamp control circuit for a short to ground or an open/high resistance.


• If one backup lamp is not illuminated test the appropriate control and ground circuits for an open/high resistance. If the circuits test normal replace the appropriate backup lamp bulb.

5. If all circuits test normal, test or replace the park neutral position or backup lamp switch.



Repair Instructions

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

* Park/Neutral Position and Backup Lamp Switch Replacement (3.7L) (Service and Repair)Park/Neutral Position and Backup Lamp Switch Replacement (5.3L) (Service and Repair)
* Park/Neutral Position and Backup Lamp Switch Adjustment (Adjustments)
* Backup Lamp Switch Replacement (Service and Repair)
* Backup Lamp Bulb Replacement (Service and Repair)