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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 positive voltage to the stop lamps, transmission control module (TCM), engine control module (ECM), and stop lamp relay coil. The BCM also supplies the stop lamp relay coil with ground. When the stop lamp relay receives battery voltage and ground from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage to the center high mounted stop lamp (CHMSL).

Reference Information

Schematic Reference

Exterior Lights Schematics Exterior Lights Schematics

Connector End View Reference

Component Connector End Views Folding Top 5 Bow Lowered Switch (CM7)

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 Stop Lamp Relay Command parameter while applying and releasing the brake pedal. The parameter should change between OFF and ON when changing between the selected stated.

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

2. Command the Stop Lamp Relay Control ON and OFF with a scan tool. The left and right rear stop lamps should turn ON and OFF when changing between the commanded states.

• If the left or right rear stop lamps do not illuminate when commanded, refer to Stop Lamp Malfunction.

3. Observe the center high mounted stop lamp while pressing and releasing the brake pedal. The center high mounted stop lamp should turn ON and OFF when changing between the selected states.

• If the center high mounted stop lamp does not change between the selected states, refer to Center High Mounted 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 OFF, verify that a test lamp illuminates between B+ and the appropriate low reference circuit terminal listed below.

* Low reference terminal 2 - with MYC

* Low reference terminal A - with MN6

• 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 appropriate 5 V reference circuit terminal listed below and ground.

* 5 V reference terminal 1 - with MYC

* 5 V reference terminal C - with MN6

• 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, test or replace the brake pedal position sensor.

Stop Lamp Malfunction

1. Ignition OFF, disconnect the stop lamp relay.

2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 30 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 87 for a short to ground. If the circuit tests normal, test or replace the stop lamp relay.

3. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.

• If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

4. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.

5. Command the Stop Lamp Relay Control 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 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.

6. Verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

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

7. Ignition OFF, disconnect the harness connector at the stop lamp.

8. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 10 ohms between the stop lamp ground circuit terminal 1 and ground.

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

9. Connect the harness connector at the stop lamp.

10. Ignition ON, connect a 15 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the stop lamp is activated.

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

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

Center High Mounted Stop Lamp Malfunction

1. Ignition OFF, disconnect the stop lamp relay.

2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 30 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 87 for a short to ground. If the circuit tests normal, test or replace the stop lamp relay.

3. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.

• If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

4. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.

5. Command the Stop Lamp Relay Control 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 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.

6. Verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

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

7. Ignition OFF, disconnect the harness connector at the center high mounted stop lamp.

8. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 10 ohms between the stop lamp ground circuit terminal A and ground.

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

9. Connect the harness connector at the center high mounted stop lamp.

10. Ignition ON, connect a 15 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the center high mounted stop lamp is activated.

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

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

Repair Instructions

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

* High Mount Stop Lamp Replacement (ZR1) High Mount Stop Lamp Replacement (ZR1)High Mount Stop Lamp Replacement (Z06) High Mount Stop Lamp Replacement (Z06)

* Tail Lamp Replacement Service and Repair

* Brake Pedal Position Sensor Calibration

* Brake Pedal Position Sensor Replacement

* Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)

* Tail Lamp Bulb Replacement Service and Repair

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

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