Circuit/System Testing

Stop Lamp Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
2. Ignition ON, test for battery voltage between the 12-volt reference circuit terminal C and ground.
   • If less than the specified range, test the 12-volt 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 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 3A fused jumper wire between the signal circuit terminal D and the 12-volt 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 stop lamp B+ terminal 4 and ground.
   • If the test lamp does not illuminate, and the STOP LAMPS fuse tests normal, test the B+ circuit for a short to ground or an open/high resistance.
3. Connect the harnes connector X4 at the BCM.
4. Ignition OFF, disconnect the harness connector at the appropriate stop lamp.
5. Test for less than 5.0 ohms between the listed ground circuit terminal below and ground.
   • Tail/Stop and Turn Signal Lamp - Left and Right - Upper and Lower terminal GRD - with Z75 - E52
   • Tail Lamp Circuit Board - Left and Right terminal D - with Z75 + E52 and European
   • Tail/Stop Lamp - Left and Right terminal GRD - with X88
   • Tail/Stop Lamp - Left and Right terminal G - Z88
   • 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 terminal and ground circuit terminal.
   • Tail/Stop and Turn Signal Lamp - Left and Right - Upper and Lower terminal MJR - with Z75 - E52
   • Tail Lamp Circuit Board - Left and Right terminal E - with Z75 + E52 and European
   • Tail/Stop Lamp - Left and Right terminal MJR - with X88
   • Tail/Stop Lamp - Left and Right terminal A - Z88
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 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 appropriate stop lamp.

CHMSL Malfunction

1. Ignition OFF, disconnect the harness connector X4 at the BCM.
2. Ignition ON, verify a test lamp illuminates between the B+ circuit terminal 4 and ground.
   • If the test lamp does not illuminate, test the B+ circuit for an open/high resistance or short to ground.
3. Reconnect the harness connector X4 at the BCM.
4. Ignition OFF, disconnect the harness connector at the center high mounted stop lamp (CHMSL).
5. Test for less than 5.0 ohms between the 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 stop lamp control circuit terminal A and ground circuit terminal B.
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 CHMSL.