As the brake pedal is pressed, the switch contacts in the brake switch close allowing battery positive voltage to be supplied to the body control module (BCM), transmission control module (TCM), and the engine control module (ECM). The BCM then supplies voltage to the stop lamps, center high mounted stop lamp (CHMSL), and stop/turn lamp control circuits.

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 ON, observe the scan tool Stop Lamp Switch Status parameter while pressing and releasing the brake pedal. The reading should change between 1 count and approximately 1023 counts.

⇒	If not the specified value, refer to the Stop Lamp Switch Malfunction.

2. Ignition ON, observe the left, right and center high mount stop lamps while pressing and releasing the brake pedal. The stop lamps should turn ON and OFF.

⇒	If the left and or right stop lamps or center high mount stop lamp are always on or inoperative, refer to the Stop Lamp Malfunction

Stop Lamp Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal B and ground.

⇒	If less than the specified range, test the ignition circuit for a short to ground or an open/high resistance.

3. Verify the scan tool Stop Lamp Switch Status parameter is approximately 1023 counts.

⇒	If not the specified value, test the signal circuit terminal A for a short to voltage. If the circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the signal circuit terminal A and the ignition circuit terminal B. Verify the scan tool Stop Lamp Switch Status parameter is 1 count.

⇒	If not the specified value, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the BCM.

5. If all circuits test normal, test or replace the stop lamp switch.

Stop Lamp Malfunction

1. Ignition OFF, disconnect the X4 harness connector at the BCM.
2. Ignition ON, verify a test lamp illuminates between the terminals listed below and ground.

•	Terminal 1

•	Terminal 2

•	Terminal 4

⇒	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 BCM.
4. Ignition OFF, disconnect the harness connector at the inoperative stop lamp.
5. Verify that a test lamp illuminates between the listed ground circuit terminal and ground.

•	Tail/Stop Lamp terminal B

•	CHMSL terminal B

•	Turn Signal 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 listed stop lamp control circuit terminals below and ground.

•	Tail/Stop Lamp terminal C

•	CHMSL terminal A

•	Turn Signal Lamp terminal A

7. 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 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.

8. If all circuits test normal, test or replace the inoperative stop lamp.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.