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 voltage to the center high mounted stop lamp (CHMSL) relay coil. When the CHMSL relay receives voltage from the BCM, the relay coil is energized and the CHMSL relay switch contacts close applying battery voltage to the CHMSL, transmission control module (TCM), and engine control module (ECM).
Reference Information
Schematic Reference
Exterior Lights Schematics (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
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 ON and Off as the brake pedal is applied and released.
• If the parameter does not change between the selected states, refer to Brake Pedal Position Sensor Malfunction.
2. With a scan tool, command the LR Stop/Turn Signal Lamp ON and OFF. The left rear turn signal should turn ON and OFF when changing between the commanded states.
• If the left rear stop lamp does not turn ON and OFF as commanded, refer to Stop Lamps Malfunction.
3. With a scan tool, command the RR Stop/Turn Signal Lamp ON and OFF. The right rear turn signal should turn ON and OFF when changing between the commanded states.
• If the right rear stop lamp does not turn ON and OFF as commanded, refer to Stop Lamps Malfunction.
4. Turn the center high mounted stop lamp ON and OFF by applying and releasing the brake pedal. The center high mounted stop lamp should turn ON and OFF as the brake pedal is applied and released.
• If the center high mounted stop lamp does not turn ON and OFF as selected, 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 ON, verify that a test lamp does not illuminate between the low reference circuit terminal C 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 A 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 Lamps Malfunction
1. Ignition OFF, disconnect the harness connector at the appropriate tail/stop and turn signal lamp.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohm between the ground circuit terminal listed below and ground.
* Tail/stop and turn signal lamp - terminal C (coupe)
* Tail/stop and turn signal lamp - terminal G (sedan)
• 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 tail/stop and turn signal lamp.
Center High Mounted Stop Lamp Malfunction
1. Ignition OFF, disconnect the CHMSL relay.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohm between the ground circuit terminal 86 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 87 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 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 CHMSL relay.
5. Ignition OFF, disconnect the harness connector at the CHMSL.
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 CHMSL.
8. Connect a 10 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the CHMSL is illuminated.
• If the CHMSL does not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the CHMSL.
9. Connect a test lamp between the control circuit terminal 85 and ground.
10. Ignition ON, turn 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 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, replace the CHMSL relay.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Brake Pedal Position Sensor Replacement (Brake Pedal Position Sensor Replacement)
* High Mount Stop Lamp Replacement (Service and Repair)
* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))
* Tail Lamp Replacement (Chevrolet Coupe) (Tail Lamp Replacement (Coupe))Tail Lamp Replacement (Chevrolet, Pontiac Sedan) (Tail Lamp Replacement (Sedan))Tail Lamp Replacement (Chevrolet European) (Tail Lamp Replacement (European))
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming