B2550

DTC B2550

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.

DTC Descriptor
DTC B2550 00
- Backup Lamps Control Circuit

Diagnostic Fault Information





Circuit/System Description

When the transmission is placed in the REVERSE position, the engine control module (ECM) sends a GMLAN serial data message to the body control module (BCM). The message indicates that the gear selector is in the REVERSE position. The BCM sends battery voltage to the backup lamps and the inside rearview mirror. The backup lamps are permanently grounded at G401 for the left and G402 for the right or G305 depending on the model. Once the driver moves the gear selector out of the REVERSE position, a message is sent by the TCM via serial data requesting the BCM to remove battery voltage from the backup lamp control circuit. Reference Information

Conditions for Running the DTC

The battery voltage must be between 9-16 volts.

Conditions for Setting the DTC

* When the BCM receives a backup lamp request signal and the backup lamp supply voltage circuit is shorted to ground.
* When the BCM is not receiving a backup lamp request signal and the backup lamp supply voltage circuit is open or shorted to voltage.

Action Taken When the DTC Sets

The backup lamps will be inoperative or always on.

Conditions for Clearing the DTC

* This DTC will clear on current status after the condition for setting the fault is corrected.
* A history DTC will clear after 100 consecutive ignition cycles without a fault present.

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 harness connector at the inoperative backup lamp.
2. Test for less than 5.0 ohms between the listed ground circuit terminal and ground.

* Backup Lamp terminal E - Chevy, Isuzu
* Backup Lamp terminal G - GMC

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

3. Connect a test lamp between the listed control circuit terminal and ground circuit terminal.

* Backup Lamp terminal C - Chevy, Isuzu
* Backup Lamp terminal A - GMC

4. 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. If all circuits test normal, test or replace the inoperative backup lamps.

Repair Instructions

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

* Backup Lamp Bulb Replacement (GMC) ()
* Control Module References (Programming and Relearning) for BCM replacement, programming, and setup.