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-volt 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 lamp control circuit illuminating the left and right stop lamps and the center high mounted stop lamp (CHMSL). The BCM also applies battery voltage to the engine control module (ECM) via the brake applied signal circuit.
Reference Information
Schematic Reference
* Exterior Lights Schematics Exterior Lights Schematics
* Body Control System Schematics [1][2]Body Control Systems
Connector End View Reference
Component Connector End Views Fuel Pump and Level Sensor Assembly
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
Ignition ON, observe the scan tool Brake Status parameter as you apply and un apply 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 (BPP) Sensor Malfunction.
If the parameter changes as the brake pedal is applied and released, refer to Stop Lamps Malfunction.
Circuit/System Testing
Stop Lamps Malfunction
1. Ignition OFF, disconnect the X4 harness connector at the K9 body control module.
2. Verify that a test lamp illuminates between the B+ circuit terminal 4 and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
3. Connect the X4 harness connector at the K9 body control module.
4. Disconnect the harness connector at the inoperative stop lamp.
5. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground:
* E42L tail lamp assembly - terminal GRD
* E42R tail lamp assembly - terminal GRD
* E6 center high mounted stop lamp - terminal B
• If greater than the specified range, test the ground circuit for an open/high resistance.
6. Connect a test lamp between the appropriate control circuit terminal listed below and ground:
* E42L tail lamp assembly - terminal 4
* E42R tail lamp assembly - terminal 4
* E6 center high mounted stop lamp - terminal A
7. Ignition ON, command the Brake Light Test 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 K9 body control module.
• 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 K9 body control module.
8. If all circuits test normal, replace the inoperative stop lamp.
Brake Pedal Position Sensor Malfunction
1. Ignition OFF, disconnect the harness connector at the B22 brake pedal position sensor.
2. Ignition ON, verify that a test lamp illuminates between the low reference circuit terminal C and B+.
• If the test lamp does not illuminate, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 body control module.
3. Ignition ON, test for 4.8 volts and 5.2 volts between the 5-volt reference circuit terminal A and ground.
• If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 body control module.
• If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the K9 body control module.
4. If all circuits test normal, replace the B22 brake pedal position sensor.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* High Mount Stop Lamp Replacement Service and Repair
* Stop and Tail Lamp Bulb Replacement Stop and Tail Lamp Bulb Replacement
* Stop Lamp Switch Replacement Service and Repair
* Control Module References Control Module References for BCM replacement, setup, and programming