Battery voltage is applied at all times to the body control module (BCM) from the BACKUP/STOP fuse located in the underhood fuse block. When the brake pedal is applied and the BCM receives a brake applied signal from the stop lamp switch. It then applies battery voltage through the CHMSL supply voltage circuit illuminating the CHMSL.

The BCM detects a short to ground on the CHMSL supply voltage circuit when the stop lamps are commanded ON.

The BCM will deactivate power to the CHMSL.

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, disconnect the X4 harness connector at the BCM.
2. Ignition ON, 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. Ignition OFF, connect the X4 harness connector at the BCM and disconnect the harness connector at the CHMSL.
4. Test for less than 5.0 ohms between the ground circuit terminal B and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

5. Connect a test lamp between the control circuit terminal A and ground.
6. Ignition ON, press and release the brake pedal. The test lamp should turn ON and OFF when pressing and releasing the brake pedal.

⇒	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.

7. If all circuits test normal, test or replace the CHMSL.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.