Circuit/System Testing

Fog Lamp Relay Circuit Testing 

1. Ignition OFF, disconnect the fog lamp relay, underhood fuseblock terminal C2 pin 19.
2. Ignition ON, verify that a test lamp illuminates between the underhood fuseblock B+ circuit and ground.
   • If the test lamp does not illuminate, repair the voltage supply circuit for a short to ground or an open/high resistance. If the voltage supply circuit fuse is open, test the relay switch control circuit underhood fuseblock terminal C3 pin 4 for a short to ground. If the circuit tests normal, replace the underhood fuseblock.
3. Disconnect the harness connector at the fog lamp bulbs.
4. Test for less than 1 Ω of resistance between the fog lamp bulb ground circuit and ground
   • If greater than 1 Ω, test the ground circuit for an open/high resistance
5. Connect the harness connector at the fog lamp bulbs.
6. Connect a 10-amp fused jumper wire between the relay switch voltage supply circuit and the fog lamp signal circuit. Verify the fog lamps are activated.
   • If the fog lamps are not activated, test the fog lamp signal circuit for a short to ground or an open/high resistance.
7. Connect a test lamp between the relay coil control circuit BCM terminal C4 pin 11 and the underhood fuseblock B+ circuit.
8. Turn the fog lamp relay ON and OFF by turning ON and OFF the fog lamp switch. The test lamp should turn ON and OFF when changing between the commanded states.
   • If the test lamp remains ON all the time, test for a short to ground on the relay coil control circuit. If the circuit tests normal, replace the BCM.
   • If the test lamp remains OFF all the time, test for a short to voltage or an open/high resistance on the relay coil control circuit. If the circuit tests normal, replace the BCM.
9. If all circuits test normal, test or replace the underhood fuseblock.

Fog Lamp Switch Circuit Testing 

1. Ignition OFF, disconnect the harness connector at the fog lamp switch, pin 4.
2. Ignition OFF, test for less than 1 Ω of resistance between the ground circuit and ground.
   • If greater than 1 Ω, test the ground circuit for an open/high resistance. If the circuit test normal, replace the BCM.
3. Verify the scan tool fog lamp switch parameter is inactive.
   • If not inactive, test the signal circuit for a short to ground. If the circuit tests normal, replace the BCM.
4. Install a 3-amp fused jumper wire between the signal circuit and ground. Verify the scan tool fog lamp switch parameter is active.
   • If not active, test the signal circuit of the fog lamp switch for a short to voltage or an open/high resistance. If circuit tests normal, replace the BCM.
5. If all circuits test normal, test or replace the head lamp switch located within the multifunction switch.

Fog Lamp Switch Testing 

1. Ignition OFF, disconnect the harness connector at the headlamp switch, pin 4.
2. Test for infinite resistance between the signal terminal and the voltage supply terminal with the switch in the open position.
   • If less than infinite resistance, replace the headlamp switch located within the multifunction switch.
3. Test for less than 1.5 ohms between the signal terminal and the voltage supply terminal with the switch in the closed position.
   • If greater than 1.5 ohms, replace the headlamp switch located within the multifunction switch.