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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 battery voltage to the right and left stop lamp control circuits, transmission control module (TCM), engine control module (ECM), and center high mounted stop lamp (CHMSL) control circuit.

Reference Information

Schematic Reference

Exterior Lights Schematics Exterior Lights Schematics

Connector End View Reference

Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)

Description and Operation

Exterior Lighting Systems Description and Operation Exterior Lighting Systems

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

Control Module References Control Module References for scan tool information

Circuit/System Verification

1. Ignition ON, observe the scan tool Brake Applied Output Signal parameter while pressing and releasing the brake pedal. The parameter should change between ON and OFF as the brake pedal is applied and released.

• If the parameter does not change between the selected states, refer to the Brake Pedal Position Sensor Malfunction.

2. Observe the left and right stop lamps while applying and releasing the brake pedal. The stop lamps should turn ON and OFF as the brake pedal is applied and released.

• If the left or right stop lamps do not change between the selected states, refer to the Stop Lamp Malfunction.

3. Observe the center high mount stop lamp while pressing and releasing the brake pedal. The center high mount stop lamp should turn ON and OFF as the brake pedal is applied and released.

• If the center high mount stop lamp does not change between the selected states, refer to Center High Mount Stop Lamp Malfunction.

Circuit/System Testing

Brake Pedal Position Sensor Malfunction

1. Ignition OFF, disconnect the harness connector at the brake pedal position sensor.

2. Ignition ON, verify that a test lamp does not illuminate between the low reference circuit terminal 2 and ground.

• If the test lamp illuminates, test the low reference circuit for a short to voltage. If the circuit tests normal, replace the BCM.

3. Ignition ON, test for 4.8 V and 5.2 V between the 5 V reference circuit terminal 1 and ground.

• 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.

• 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.

4. If all circuits test normal, replace the brake pedal position sensor.

Stop Lamp Malfunction

1. Ignition OFF, disconnect the X4 harness connector at the BCM.

2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminals listed below and ground:

* Terminal 1

* Terminal 2

* Terminal 4

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

3. Ignition OFF, connect the X4 harness connector at the BCM.

4. Disconnect the harness connector at the appropriate stop lamp.

5. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal GRD and ground.

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

6. Connect a test lamp between the stop lamp control circuit terminal MJR and ground.

7. Ignition ON, command the stop lamps ON and OFF by applying and releasing the brake pedal. 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 inoperative stop lamp.

Center High Mount Stop Lamp Malfunction

1. Ignition OFF, disconnect the X5 harness connector at the fuse block - underhood.

2. Connect a test lamp between the control circuit terminal K6 and B+.

3. Ignition ON, command the stop lamps ON and OFF by applying and releasing the brake pedal. 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 ground. If the circuit tests normal, replace the BCM.

• If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

4. Ignition OFF, connect the X5 harness connector at the fuse block - underhood. Disconnect the harness connector at the center high mount stop lamp.

5. Disconnect the harness connector at the center high mount stop lamp.

6. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal B and ground

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

7. Connect a test lamp between the control circuit terminal A and ground.

8. Ignition ON, command the stop lamps ON and OFF by applying and releasing the brake pedal. 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 fuse block - underhood.

• 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 fuse block - underhood.

9. If all circuits test normal, replace the center high mount stop lamp.

Repair Instructions

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

* High Mount Stop Lamp Replacement (Extended and Crew Cab) High Mount Stop Lamp Replacement (Extended and Crew Cab)High Mount Stop Lamp Replacement (Regular Cab) High Mount Stop Lamp Replacement (Regular Cab)

* Tail Lamp Bulb Replacement (Chevrolet) Service and RepairTail Lamp Bulb Replacement (GMC) Service and Repair

* Tail Lamp Replacement (Chevrolet) Service and RepairTail Lamp Replacement (HD) Service and RepairTail Lamp Replacement (GMC) Service and Repair

* Brake Pedal Position Sensor Calibration

* Control Module References Control Module References for BCM replacement, programming, and setup.

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