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 side. When the stop lamp relay receives battery voltage from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage through the STOP LP fuse to illuminate 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 (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 as you apply and unapply the brake pedal. The parameter should change between Off and On as the brake pedal is applied and released.
• If the parameter does not change as the brake pedal is applied and released, refer to Brake Pedal Position Sensor Malfunction.
2. With a scan tool, command the LR Stop/Turn Signal Lamp On and Off. The LR turn signal should turn On and Off when changing between the commanded states.
• If the LR stop lamp does not illuminate when commanded, refer to Stop Lamps Malfunction.
3. With a scan tool, command the RR Stop/Turn Signal Lamp On and Off. The RR turn signal should turn On and Off when changing between the commanded states.
• If the RR stop lamp does not illuminate when commanded, refer to Stop Lamps Malfunction.
4. Command 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 when changing between the commanded states.
• If the center high mounted stop lamp does not illuminate when commanded, 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 stop lamp.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohm between the appropriate ground circuit terminal listed below and ground.
* Left tail lamp ground terminal 3 - uplevel
* Left stop/tail/turn signal ground terminal C - base
* Right tail lamp ground terminal 3 - uplevel
* Right stop/tail/turn signal ground terminal C - base
• If greater than the specified range, test the ground circuit for an open/high resistance.
3. Connect a test lamp between the appropriate control circuit terminal listed below and ground.
* Left stop/turn signal control terminal 2 - uplevel
* Left stop/turn signal control terminal A - base
* Right stop/turn signal control terminal 2 - uplevel
* Right stop/turn signal control terminal A - base
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 lamp assembly.
Center High Mounted Stop Lamp Malfunction
1. Ignition OFF, disconnect the stop lamp relay.
2. Ignition ON, headlamps ON, test for less than 1 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 stop lamp relay.
5. Ignition OFF, disconnect the harness connector at the center high mounted 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 mounted stop lamp.
8. Connect a 10 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the center high mounted stop lamp is illuminated.
• If the center high mounted stop lamp does not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the center high mounted stop lamp.
9. Connect a test lamp between the control circuit terminal 85 and ground.
10. 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.
11. If all circuits test normal, test or replace the center high mounted stop lamp.
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 (LS/LT) (Tail Lamp Replacement (LS/LT))Tail Lamp Replacement (LTZ) (Tail Lamp Replacement (LTZ))
* Tail Lamp Bulb Replacement (LS/LT) (Service and Repair)
* Brake Pedal Position Sensor Replacement ()
* Brake Pedal Position Sensor Calibration ()
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming