Buick Regal: Backup Lamps Malfunction

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

1. Reverse gear lamp inoperative
2. Reverse gear lamp always ON

Circuit/System Description

When the transmission is placed in the reverse position, the engine control module (ECM) 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. The backup lamps are permanently grounded. Once the driver moves the gear selector out of the reverse position, a message is sent by the ECM via serial data requesting the BCM to remove battery voltage from the backup lamp control circuit.

Reference Information

Schematic Reference

Exterior Lights Wiring Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information.

Circuit/System Verification

Ignition ON, perform the Backup Lamps test. The backup lamp should be ON/OFF.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the B16 Backup Lamp Switch.

2. Test for less than 5 Ω between the ground circuit harness connector terminal 2 and ground.

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

3. Disconnect the X1 harness connector at the K20 Engine Control Module.

4. Ignition ON, test for less than 0.3 V at the B16 Backup Lamp Switch signal circuit harness connector terminal 1 and ground.

• If greater than the specified value, test the signal circuit for a short to voltage.

5. Ignition OFF, test for infinite resistance between the B16 Backup Lamp Switch signal circuit harness connector terminal 1 and ground.

• If lower than the specified value, test the signal circuit for a short to ground.

6. Connect the harness connector at the B16 Backup Lamp Switch.

7. Reversing gear engaged, test for less than 5 Ω between the K20 Engine Control Module X1 harness connector terminal 71 and ground.

• If greater than the specified value, test the signal circuit for an open/high resistance. If the circuit tests normal, test or replace the B16 Backup Lamp Switch.

8. Reversing gear disengaged, test for infinite resistance between the K20 Engine Control Module X1 harness connector terminal 71 and ground.

• If lower than the specified value, test or replace the B16 Backup Lamp Switch.

9. If all the circuits test normal, replace the K20 Engine Control Module.

Component Testing

Static Test

1. Ignition OFF, disconnect the harness connector at the B16 Backup Lamp Switch. Reversing gear engaged, test for less than 5 Ω at the B16 Backup Lamp Switch terminal 1 and terminal 2.

• If greater than the specified value replace the B16 Backup Lamp Switch.

2. Reversing gear disengaged, test for infinite resistance at the B16 Backup Lamp Switch terminal 1 and terminal 2.

• If less than the specified value replace the B16 Backup Lamp Switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• Tail Lamp Replacement (5-Door Hatchback 68) Tail Lamp Replacement (5-Door Wagon 35)
• Control Module References for BCM replacement, setup and programming

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