Buick Regal: Stop 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. Stop Lamps Malfunction
2. Center High Mounted Stop Lamp Malfunction

Circuit/System Description

The brake pedal position sensor is used to sense the action of the driver application of the brake pedal.

The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The body control module (BCM) provides a low reference signal and a 5 V reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery voltage to the left and right stop lamp control circuits as well as the center high mounted stop lamp control circuit illuminating the left and right stop lamps and the center high mounted stop lamp.

Diagnostic Aids

When testing at the stop lamp bulb sockets, make sure all measurements and test lamp connections are in the correct terminal location and do not come in contact with each other during testing.

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

1. Ignition ON.

2. Verify the scan tool Brake Pedal Applied parameter changes between Active and Inactive while pressing and releasing the brake pedal.

• If the parameter does not change

Refer to Circuit/System Testing - Brake Pedal Position Sensor Malfunction.

• Go to next step: If the parameter changes

3. Verify the left brake lamp turns ON and OFF when commanding the Left Stop Lamp ON and OFF with a scan tool.

• If the left brake lamp does not turn ON and OFF

Refer to Circuit/System Testing - Stop Lamps Malfunction.

• Go to next step: If the left brake lamp turns ON and OFF

4. Verify the right brake lamp turns ON and OFF when commanding the Right Stop Lamp ON and OFF with a scan tool.

• If the right brake lamp does not turn ON and OFF

Refer to Circuit/System Testing - Stop Lamps Malfunction.

• Go to next step: If the right brake lamp turns ON and OFF

5. Verify the center high mounted stop lamp turns ON and OFF when commanding the Center Stop Lamp ON and OFF with a scan tool.

• If the center high mounted stop does not turn ON and OFF

Refer to Circuit/System Testing - Center High Mount Stop Lamp Malfunction.

• Go to next step: If the center high mounted stop turns ON and OFF

6. All OK.

Circuit/System Testing

Brake Pedal Position Sensor Malfunction

1. Ignition OFF, disconnect the harness connector at the B22 Brake Pedal Position Sensor, ignition ON.

2. Test for less than 1 V between the low reference circuit terminal 1 and ground.

• If 1 V or greater

1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module, ignition ON.
2. Test for less than 1 V between the low reference circuit and ground.
   • If 1 V or greater, repair the short to voltage on the circuit.
   • If less than 1 V, replace the K9 Body Control Module.

• Go to next step: If less than 1 V

3. Test or replace the B22 Brake Pedal Position Sensor.

Stop Lamps Malfunction

1. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate E4 Turn Signal Lamp. It may take up to 2 min for all vehicle systems to power down.

2. Test for less than 15 Ω between the ground circuit terminal B and ground.

• If 15 Ω or greater

1. Ignition OFF.
2. Test for less than 2 Ω in the ground circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, repair the open/high resistance in the ground connection.

• Go to next step: If less than 15 Ω

3. Connect a test lamp between the control circuit terminal A and ground, ignition ON.

4. Verify the test lamp turns ON and OFF when commanding the appropriate Stop Lamp ON and OFF with a scan tool.

• If the test lamp is always OFF

1. Ignition OFF, disconnect the appropriate harness connector listed below at the K9 Body Control Module.
   • X4 left stop lamp
   • X5 right stop lamp
2. Test for infinite resistance between the control circuit and ground.
   • If less than infinite resistance, repair the short to ground on the circuit.
   • Go to next step: If infinite resistance
3. Test for less than 2 Ω in the control circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K9 Body Control Module.

• If the test lamp is always ON

1. Ignition OFF, disconnect the appropriate harness connector listed below at the K9 Body Control Module, ignition ON.
   • X4 left stop lamp
   • X5 right stop lamp
2. Test for less than 1 V between the control circuit terminal and ground.
   • If 1 V or greater, repair the short to voltage on the circuit.
   • If less than 1 V, replace the K9 Body Control Module.

• Go to next step: If the test lamp turns ON and OFF

5. Test or replace the appropriate E4 Turn Signal Lamp.

Center High Mount Stop Lamp Malfunction

1. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the E6 Center High Mounted Stop Lamp. It may take up to 2 min for all vehicle systems to power down.

2. Test for less than 15 Ω between the ground circuit terminal 2 and ground.

• If 15 Ω or greater

1. Ignition OFF.
2. Test for less than 2 Ω in the ground circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, repair the open/high resistance in the ground connection.

• Go to next step: If less than 15 Ω

3. Connect a test lamp between the control circuit terminal 1 and ground, ignition ON.

4. Verify the test lamp turns ON and OFF when commanding the Center Stop Lamp ON and OFF with a scan tool.

• If the test lamp is always OFF

1. Ignition OFF, disconnect the X4 harness connector at the K9 Body Control Module.
2. Test for infinite resistance between the control circuit and ground.
   • If less than infinite resistance, repair the short to ground on the circuit.
   • Go to next step: If infinite resistance
3. Test for less than 2 Ω in the control circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K9 Body Control Module.

• If the test lamp is always ON

1. Ignition OFF, disconnect the X4 harness connector at the K9 Body Control Module, ignition ON.
2. Test for less than 1 V between the control circuit terminal and ground.
   • If 1 V or greater, repair the short to voltage on the circuit.
   • If less than 1 V, replace the K9 Body Control Module.

• Go to next step: If the test lamp turns ON and OFF

5. Test or replace the E6 Center High Mounted Stop Lamp.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• High Mount Stop Lamp Replacement (Wagon) High Mount Stop Lamp Replacement (Hatchback)
• Brake Pedal Position Sensor Replacement
• Brake Pedal Position Sensor Calibration
• Rear Body Structure Stop Lamp Replacement (5-Door Hatchback 68) Rear Body Structure Stop Lamp Replacement (5-Door Wagon 35)
• Control Module References for BCM replacement, programming, and setup

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