The stop lamp switch is used to sense the action of the driver application of the brake pedal. The body control module (BCM) provides a low reference signal and a B+ reference voltage to the stop lamp switch. When the stop lamp switch contacts close indicating the brakes have been applied, the BCM will apply battery voltage to stop lamp relay control circuit and the center high mounted stop lamp (CHMSL). When the stop lamp relay receives battery voltage from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage to the STOP LP fuse to illuminate the left and right stop lamps.

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

Ignition ON, observe the scan tool Stop Lamp Switch Status parameter as you apply and unapply the brake pedal. The parameter should change as the brake pedal is applied and released.

Stop Lamps Malfunction

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.
4. Disconnect the stop lamp relay.
5. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal 86 and ground.

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

6. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

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

7. Verify that a test lamp illuminates between the B+ circuit terminal 30 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 87 for a short to ground. If the circuit tests normal, test or replace the stop lamp relay.

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

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

10. Connect the harness connector at the inoperative stop lamp.
11. Connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. 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, replace the inoperative stop lamp.

12. Connect a test lamp between the control circuit terminal 85 and the ground circuit terminal 86.
13. Ignition ON, command the stop lamps ON and OFF by applying and releasing 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.

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

Stop Lamp Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
2. Ignition ON, test for B+ between the B+ voltage reference circuit terminal 1 and ground.

⇒	If less than the specified value, test the B+ voltage reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

3. Ignition ON, verify the scan tool Stop Lamp Switch Status parameter displays 1 Count or less.

⇒	If greater than the specified value, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM.

4. Connect a 3A fused jumper wire between the B+ voltage reference circuit terminal 1 and the signal circuit terminal 2. Verify the scan tool Stop Lamp Switch Status parameter is greater than 1000 Counts.

⇒	If less than the specified value, test the signal 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, test or replace the stop lamp switch.

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 2 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 1 and ground.
4. Ignition ON, command the stop lamps ON and OFF by applying and releasing 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.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.