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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 stop lamps, transmission control module (TCM), engine control module (ECM), and center high mounted stop lamp (CHMSL) relay coil. When the CHMSL relay receives battery voltage from the BCM, the relay coil is energized and the CHMSL relay switch contacts close applying battery voltage through the STOP LP fuse to illuminate the CHMSL.

Reference Information
Schematic Reference

Exterior Lights Schematics (Exterior Lights Schematics)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
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 (Programming and Relearning)for scan tool information

Circuit/System Verification

1. Ignition ON, observe the scan tool Brake Lamp Cmd. parameter while applying and releasing the brake pedal. The parameter should change between OFF and ON.

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

2. Command the LR Stop/Turn Signal Lamp and RR Stop/Turn Signal Lamp ON and OFF with a scan tool. The left and right rear stop lamps should turn ON and OFF when commanded.

• If the LR or RR stop lamp does not illuminate when commanded, refer to 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.

• 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 A 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 4.8-5.2 V between the 5 V reference circuit terminal C 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 harness connector at the appropriate stop lamp.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohm between the ground circuit terminal C and ground.

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

3. Connect a test lamp between the control circuit terminal A and ground.
4. Ignition ON, command the appropriate Stop/Turn Signal Lamp 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.

5. If all circuits test normal, replace the stop lamp.

Center High Mount Stop Lamp Malfunction
1. Ignition OFF, disconnect the center high mount stop lamp relay.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohm between the ground circuit terminal 2 and ground.

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

3. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 5 and ground.

• If the test lamp illuminates, test the control circuit for a short to voltage.

4. Verify that a test lamp illuminates between the B+ circuit terminal 3 and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal 5 for a short to ground. If the circuit tests normal, test or replace the CHMSL relay.

5. Ignition OFF, disconnect the harness connector at the center high mount stop lamp.
6. Ignition OFF, exterior lamps OFF, test for less than 5 ohm 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 the harness connector at the center high mount stop lamp.
8. Connect a 10 A fused jumper wire between the B+ circuit terminal 3 and the control circuit terminal 5. Verify the center high mount stop lamp illuminates.

• If the center high mount stop lamp does not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the center high mount stop lamp.

9. Connect a test lamp between the control circuit terminal 1 and ground.
10. Ignition ON, turn the test lamp ON and OFF by applying and releasing the brake pedal. The test lamp should turn ON and OFF when changing between the selected 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.

11. If all circuits test normal, test or replace the center high mount stop lamp relay.

Repair Instructions

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

* High Mount Stop Lamp Replacement (Service and Repair)
* Tail Lamp Replacement (Service and Repair)
* Tail Lamp Bulb Replacement (Service and Repair)
* Brake Pedal Position Sensor Replacement ()
* Brake Pedal Position Sensor Calibration ()
* Relay Replacement Removal and Replacement
* Control Module References (Programming and Relearning)for BCM replacement, setup, and programming

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