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Stop Lamps Malfunction




Stop 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 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 B+ to the stop lamps, center high mounted stop lamp (CHMSL), transmission control module (TCM), and engine control module (ECM). The stop lamps will not operate unless the ignition is in the ON position.

Reference Information
Schematic Reference

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 (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Programming and Relearning (Programming and Relearning) for scan tool information

Circuit/System Verification

1. Ignition ON, observe the CHMSL while pressing and releasing the brake pedal. The CHMSL should turn ON and OFF.

• If the CHMSL does not turn ON and OFF, refer to Center High Mounted Stop Lamp Circuit Test.

2. Ignition ON, observe the rear stop lamps while pressing and releasing the brake pedal. The stop lamps should turn ON and OFF.

• If the stop lamps do not turn ON and OFF, refer to Stop Lamps Circuit Test.

Circuit/System Testing

Center High Mounted Stop Lamp Circuit Test
1. Ignition OFF, disconnect the harness connector at the CHMSL.
2. Ignition OFF, test for less than 5.0 ohm between ground circuit terminal 1 and ground.

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

3. Connect a test lamp between control circuit terminal 2 and ground.
4. Ignition ON, apply and release the brake pedal. The test lamp should turn ON and OFF as the brake pedal is applied and released.

• 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, replace the CHMSL.

Stop Lamps Circuit Test
1. Ignition OFF, disconnect the harness connector at the brake pedal position sensor.
2. Verify that a test lamp illuminates between the low reference circuit terminal C and B+.

• If the test lamp does not illuminate, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the BCM.

3. Ignition ON, test for 4.8-5.2 V between the 5 V reference circuit terminal A and ground.

• If greater than the specified range, test the 5 V reference circuit for a short to voltage. If the circuit tests normal, replace the BCM.
• If less than the specified range, test the 5 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

4. Ignition OFF, disconnect harness connector at the inoperative stop/turn lamp assembly.
5. Ignition OFF, test for less than 5.0 ohm between the ground circuit listed below and ground:

* RPO Z88 - terminal D
* All others - terminal B

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

6. Connect a test lamp between the control circuit listed below and ground:

* RPO Z88 - terminal E
* All others - terminal A

7. Ignition ON, command the appropriate LR or RR Turn Signal 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.

8. If all circuits test normal, replace the stop/turn signal lamp assembly.

Repair Instructions

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

* Brake Pedal Position Sensor Replacement ()
* High Mount Stop Lamp Replacement (Acadia) (Service and Repair) High Mount Stop Lamp Replacement (Enclave) (Service and Repair) High Mount Stop Lamp Replacement (Traverse) (Service and Repair)
* Tail Lamp Replacement (Acadia) (Service and Repair) Tail Lamp Replacement (Enclave) (Service and Repair) Tail Lamp Replacement (Traverse) (Service and Repair)
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming

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