Circuit/System Testing

Stop Lamp Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
2. Ignition ON, test for B+ between the 12 V reference circuit terminal C and ground.
   • If less than the specified range, test the 12 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
3. Verify the scan tool BCM Stop Lamp Switch Status parameter is approximately 1023 counts.
   • If not the specified value, test the signal circuit terminal D for a short to voltage. If the circuit tests normal, replace the BCM.
4. Install a 3 A fused jumper wire between the signal circuit terminal D and the 12 V reference circuit terminal C. 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 harness connector X4 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 an open/high resistance or short to ground.
3. Connect the harness connector X4 at the BCM.
4. Ignition OFF, disconnect the harness connector at the appropriate stop lamp.
5. Test for less than 1 Ω between the ground circuit terminal GRD and ground.
   • If greater than the specified range, test the ground circuit for an open/high resistance.
6. Connect a test lamp between the stop lamp control circuit terminal MJR and ground.
7. Ignition ON, press and release the brake pedal. The test lamp should turn ON and OFF when changing between the selected 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.
8. If all circuits test normal, test or replace the stop lamp.

Center High Mount Stop Lamp Malfunction

1. Ignition OFF, disconnect the X5 harness connector at the fuse block - underhood.
2. Connect a test lamp between the control circuit terminal J4 and B+.
3. Turn the center high mounted stop lamp ON and OFF by pressing and releasing the brake pedal. The test lamp should turn ON and OFF when changing between the selected 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.
4. Ignition OFF, connect the X5 harness connector at the fuse block - underhood. Disconnect the harness connector at the center high mount stop lamp.
5. Test for less than 5 Ω between the center high mount stop lamp ground circuit terminal B and ground
   • If greater than the specified range, test the ground circuit for an open/high resistance.
6. Connect a test lamp between the control circuit terminal A and ground.
7. Turn the center high mounted stop lamp ON and OFF by pressing 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 fuse block - underhood.
   • If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the fuse block - underhood.
   • If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the center high mount stop lamp.
8. If all circuits test normal, test or replace the center high mount stop lamp.