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. |
Diagnostic 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
Ground is applied at all times to the CHMSL relay coil. Upon brake activation, the body control module (BCM) applies voltage to the CHMSL relay control circuit to the coil side of the relay, energizing the relay. 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.
Reference Information
Schematic Reference
Connector End View Reference
Lighting Systems Connector End Views
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
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.
- Ignition OFF, reconnect the X5 harness connctor to the underhood fuse block. Disconnect the harness connector at the center high mounted stop lamp (CHMSL).
- Test for less than 1.0 ohm of resistance between the ground circuit terminal B and ground.
- Connect a test lamp between the CHMSL control circuit terminal A and ground.
- 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 CHMSL.
| ⇒ | 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. |
| ⇒ | If greater than the specified range, test the ground circuit for and open/high resistance. |
| ⇒ | If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block. |
| ⇒ | If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, replace the underhood fuse block. |
| ⇒ | If the test lamp is always OFF and the circuit fuse is open, test the control circuit for an short to ground. If the circuit tests normal, replace the CHMSL. |
Component Testing
Center High Mounted Stop Lamp (CHMSL)
- Ignition OFF, disconnect the harness connector at the CHMSL.
- Install a 15A fused jumper wire between the control circuit terminal A and 12 volts. Install a jumper wire between the ground circuit terminal B and ground. Verify that the CHMSL illuminates.
| ⇒ | If the CHMSL does not completely illuminate, test or replace the inoperative bulb or CHMSL. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, setup and programming |
