The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The body control module (BCM) provides a low reference signal and a 5-volt reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery positive voltage to the stop lamps, transmission control module (TCM), engine control module (ECM), and stop lamp relay coil. The BCM also supplies the stop lamp relay coil with ground. When the stop lamp relay receives battery voltage and ground from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage to the center high mounted stop lamp (CHMSL). Ground for the stop lamps and CHMSL are provided at G302.

Important: The stop lamps will not illuminate unless the ignition is in the ON position. For more detailed information concerning stop lamp operation, refer to Exterior Lighting Systems Description and Operation .

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

Scan Tool Reference

Stop Lamps Malfunction

1. Ignition OFF, disconnect harness connector at the inoperative stop lamp.
2. Test for less than 1.0 ohm of resistance between the ground circuit and ground.

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

3. Connect a test lamp between the control circuit and the ground circuit.
4. Command the stop lamp relay control ON and OFF with a scan tool. 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.

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

High Mounted Stop Lamp Malfunction

1. Ignition OFF, disconnect the stop lamp relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the B+ circuit and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the stop lamp relay.

4. Disconnect harness connector at the CHMSL.
5. Test for less than 1.0 ohm of resistance between the ground circuit terminal A and ground.

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

6. Connect the harness connector at the CHMSL.
7. Connect a 15-A fused jumper wire between the B+ circuit and the control circuit . Verify the CHMSL is activated.

⇒	If the CHMSL does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the CHMSL.

8. Connect a test lamp between the signal circuit and the relay control circuit .
9. Command the stop lamp relay control ON and OFF with a scan tool. 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 ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

10. If all circuits test normal, test or replace the stop lamp relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.