Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
TBC Fuse B+ | 1 | 1 | -- | -- |
Backup Lamp Control | B2550 00 | B2550 00 | B2550 00 | -- |
Left Backup Lamp Ground | -- | 1 | -- | -- |
Right Backup Lamp Ground | -- | 1 | -- | -- |
1. Backup Lamp Malfunction | ||||
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
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References 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 between the commanded states.
| ⇒ | If the lamps do not turn ON and OFF between the commanded states, refer to Circuit System Testing. |
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the inoperative backup lamp.
- Test for less than 5.0 ohms between the listed ground circuit terminal and ground.
- Connect a test lamp between the listed control circuit terminal and ground.
- 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 all circuits test normal, test or replace the inoperative backup lamps.
| • | 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. |
| • | Backup Lamp terminal C - Chevy, Isuzu |
| • | Backup Lamp terminal A - GMC |
| ⇒ | 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. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, programming, and setup. |
