When the fog lamp switch is placed in the ON position, ground is applied through the fog lamp switch signal circuit at G300 to the body control module (BCM). The BCM applies battery voltage through the fog lamp relay control circuit to the coil side of the fog lamp relay. Battery voltage is applied at all times from the FOG LAMP fuse to the switch side of the fog lamp relay. When the relay coil is energized, the relay switch contacts close and allow battery voltage to be applied from the FOG LAMP fuse, through the relay switch contacts, to the fog lamps. Ground for the fog lamps is applied at all times at G101 for the left fog lamp and G102 for the right fog lamp. G102 also serves as ground for the coil side of the fog lamp relay. For more detailed information concerning fog lamp operation refer to Exterior Lighting Systems Description and Operation.

Schematic Reference

Fog Lights Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

Scan Tool Reference

Ignition ON, observe the scan tool front fog lamp switch parameter while pressing and releasing the front fog lamp switch. The reading should toggle between ACTIVE and INACTIVE.

Fog Lamp Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the fog lamp switch.
2. Test for less than 1 ohm of resistance between the ground circuit terminal A and ground.

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

3. Ignition ON, verify the scan tool front fog lamp switch parameter is INACTIVE.

⇒	If not the specified value, test the signal circuit terminal C for a short to ground. If the circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the signal circuit terminal C and the ground circuit terminal A. Verify the scan tool front fog lamp switch parameter is ACTIVE.

⇒	If not the specified value, test the signal circuit terminal C for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

5. If all circuits test normal, test or replace the fog lamp switch.

Front Fog Lamps Malfunction

1. Ignition OFF, disconnect the fog lamp relay.
2. Test for less than 1 ohm of resistance between the relay coil ground circuit and ground.

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

3. Connect a test lamp between the fog lamp relay control circuit and the relay coil ground circuit.
4. Command the fog 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 BCM.

⇒	If the test lamp is always OFF, test the control circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the BCM.

5. Verify that a test lamp illuminates between the relay switch B+ circuit and ground.

⇒	If the test lamp does not illuminate, test the relay switch B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay coil B+ circuit fuse is open, test the relay controlled output circuit for a short to ground.

6. Disconnect the harness connector at the Inoperative fog lamp.
7. Test for less than 1 ohm of resistance between the inoperative fog lamp ground circuit terminal B and ground.

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

8. Connect the harness connector at the inoperative fog lamp.
9. Connect a 15A fused jumper wire between the relay switch B+ circuit and the relay controlled output circuit. Verify the fog lamps are activated.

⇒	If the fog lamps do not activate, test the relay controlled output circuit for an open/high resistance. If the circuit tests normal, test or replace the inoperative fog lamp.

10. If all circuits test normal, test or replace the fog lamp relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.