Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC B3884 00: Center High Mounted Stop Lamp (CHMSL) CircuitDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
CHMSL Relay Control | B3884 00 | 1 | 2 | -- |
CHMSL Control | 1 | 1 | 2 | -- |
CHMSL Relay Ground | -- | 1 | -- | -- |
CHMSL Ground | -- | 1 | -- | -- |
1. Center High Mounted Stop Lamp (CHMSL) Inoperative 2. Center High Mounted Stop Lamp (CHMSL) Always On | ||||
Circuit/System Description
When the brake pedal is applied, the brake pedal switch normally closed contact signal circuit voltage is interrupted to the body control module (BCM). Upon brake activation, the body control module (BCM) applies voltage through the CHMSL relay control circuit to the coil side of the relay. Ground is applied at all times to the other side of the CHMSL relay coil therefore the relay is now energized. Battery voltage is then applied through the switch side of the relay, the CHMSL fuse, and the CHMSL control circuit to the center high mounted stop lamp (CHMSL). The CHMSL is grounded at G 200.
Conditions for Running the DTC
| • | The ignition is ON. |
| • | The stop lamps must be commanded ON. |
Conditions for Setting the DTC
The BCM detects a short to ground in the CHMSL supply voltage circuit when the stop lamps are commanded ON.
Action Taken When the DTC Sets
The CHMSL does not illuminate.
Conditions for Clearing the DTC
| • | The conditions for setting the DTC are no longer present. |
| • | A history DTC clears after 100 malfunction-free ignition cycles. |
| • | The BCM receives the clear code command from the scan tool. |
Reference Information
Schematic Reference
Connector End View Reference
Lighting Systems Connector End Views
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
Ignition ON, press the brake pedal. The CHMSL should illuminate.
Circuit/System Testing
- Ignition OFF, disconnect the X5 harness connector at the underhood fuse block.
- Connect a test lamp between the CHMSL relay control circuit terminal K6 and ground at the harness connector.
- Apply the brake pedal ON and OFF. The test lamp should turn ON and OFF when changing between the commanded states.
- If all circuits test normal, test or replace the underhood fuse block.
| ⇒ | 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. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, setup, and programming |
