The brake pedal position (BPP) sensor is used to sense the action of the driver application of the brake pedal. The BPP sensor provides an analog voltage signal that will increase as the brake pedal is applied. The instrument panel module (IPM) provides a low reference signal and a 5-volt reference voltage to the BPP sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the IPM will apply battery voltage to the center high mounted stop lamp (CHMSL), transmission control module (TCM), engine control module (ECM), and stop lamp relay. When the stop lamp relay receives battery voltage from the IPM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage through the stop lamps fuse to illuminate the stop lamps. Ground for the left stop lamp and CHMSL is provided at G402 and the right stop lamp is grounded at G401.

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 Status parameter as you apply and unapply the brake pedal. The parameter should change between OFF and ON as the brake pedal is applied and released.

⇒	If the parameter does not change as the brake pedal is applied and released, refer to Brake Pedal Position Sensor (BPPS) Malfunction.

2. With a scan tool, command the Stop Lamps ON and OFF. The stop lamps should turn ON and OFF when changing between the commanded states.

⇒	If the stop lamps do not illuminate when commanded, refer to Stop Lamps Malfunction.

Stop Lamps Malfunction

1. Ignition OFF, disconnect the stop lamp relay.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal R36 and ground.

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

3. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal R38 and ground.

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

4. Verify that a test lamp illuminates between the B+ circuit terminal R37 and ground.

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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 relay control circuit terminal R38 for a short to ground. If the circuit tests normal, test or replace the stop lamp relay.

5. Disconnect the harness connector at the inoperative stop lamp.
6. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal D and ground.

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

7. Connect the harness connector at the inoperative stop lamp.
8. Connect a 10A fused jumper wire between the B+ circuit terminal R37 and the control circuit terminal R38. Verify the stop lamps are activated.

⇒	If the stop lamps do not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the inoperative stop lamp.

9. Connect a test lamp between the control circuit terminal R40 and the ground circuit terminal R36.
10. Ignition ON, command the Stop Lamps 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 IPM.

⇒	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 IPM.

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

Center High Mounted Stop Lamp (CHMSL) Malfunction

1. Ignition OFF, disconnect the harness connector at the CHMSL.
2. Ignition OFF, exterior lamps OFF, test for less than 5 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 control circuit terminal A and the ground circuit terminal B.
4. Ignition ON, command the Stop Lamps 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 IPM.

⇒	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 IPM.

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

Brake Pedal Position Sensor (BPPS) Malfunction

1. Ignition OFF, disconnect the harness connector at the BPPS.
2. Ignition ON, verify that a test lamp does not illuminate between the low reference circuit terminal A and ground.

⇒	If the test lamp illuminates, test the low reference circuit for a short to voltage. If the circuit tests normal, replace the IPM.

3. Ignition ON, test for 4.8 volts and 5.2 volts between the 5-volt reference circuit terminal C and ground.

⇒	If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the IPM.

⇒	If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the IPM.

4. If all circuits test normal, replace the BPPS.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.