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.

The BCM detects a short to ground in the CHMSL relay control circuit when the stop lamps are commanded ON.

The CHMSL does not illuminate.

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 harness connectors at the center high mounted stop lamp.
2. 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.

3. Connect a test lamp between the stop lamp control circuit terminal A and ground circuit terminal B.
4. Ignition ON, press and release 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 test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance.

5. If all circuits test normal, test or replace the center high mounted stop lamp.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.