The body control module (BCM) controls the fog lamps based on inputs from the fog lamp switch. When the fog lamp switch is pressed, a ground path is provided on the front fog lamp switch signal circuit to the BCM, indicating the front fog lamps ON command. In response to this signal, the BCM grounds the fog lamp relay control circuit energizing the FOG LAMP PCB Relay. With the fog lamp relay energized, battery voltage is applied through the FOG Fuse and the fog lamp supply voltage circuits illuminating the front fog lamps.

When a fog lamp request is seen by the BCM, a serial data message is sent to the instrument panel cluster (IPC) requesting the fog lamp indicator be illuminated.

Schematic Reference

Fog Lights Schematics

Connector End View Reference

Lighting Systems Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

1. Observe the scan tool Front Fog Lamps Switch parameter while pressing and releasing the fog lamp switch. The parameter should cycle between Active and Inactive.

⇒	If the parameter does cycle between the specified values, refer to Fog Lamp Switch Circuit Test.

2. With a test lamp connected to ground, probe each of the test points on the FOG Fuse while commanding the Fog Lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF at one or both of the fuse test points when changing between commanded states.

⇒	If the test lamp is always OFF, or remains always ON, refer to Fog Lamp PCB Relay Circuit Test.

⇒	If the test lamp turns ON and OFF, refer to Fog Lamps Circuit Test

3. With the fog lamps ON, verify the fog lamp indicator is illuminated on the IPC.

⇒	If the indicator does not illuminate, refer to Front Fog Lamp Indicator Test.

Fog Lamp Switch Circuit Test

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Verify that a test lamp illuminates between the ground circuit terminal 8 and B+.

⇒	If the test lamp does not illuminate, 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 6 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 6 and the ground circuit terminal 8. Verify the scan tool Front Fog Lamp Switch parameter is Active.

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

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

Fog Lamp PCB Relay Circuit Test

1. Ignition OFF, disconnect the (C2) harness connector at the underhood fuse block.
2. Connect a test lamp between B+ and the control circuit terminal 23.
3. Ignition ON, 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 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. If all circuits test normal, replace the underhood fuse block.

Fog Lamps Circuit Test

1. Ignition OFF, disconnect the harness connector at the inoperative fog lamp.
2. Test for less than 5.0 ohms of resistance between the ground circuit terminal B and ground.

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

3. Connect a test lamp between the supply voltage circuit terminal A and ground.
4. Ignition ON, 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 supply voltage circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block.

⇒	If the test lamp is always OFF, test the supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

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

Front Fog Lamp Indicator Test

1. Ignition ON, with a scan tool perform the display test for the instrument panel cluster (IPC) and observe the front fog lamp indicator.

⇒	If the front fog lamp indicator illuminates during the test, replace the BCM.

⇒	If the front fog lamp indicator does not illuminate during the test or remains illuminated at all times, replace the IPC.

Headlamp Switch

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Test for infinite resistance between the signal circuit terminal 6 and the ground circuit terminal 8 with the switch in the open position.

⇒	If not the specified value, replace the headlamp switch.

3. Test for less than 2.0 ohms of resistance between the signal circuit terminal 6 and the ground circuit terminal 8 with the switch in the closed position.

⇒	If greater than the specified range, replace the headlamp switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.