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 Relay. With the fog lamp relay energized, battery voltage is applied through the FOG LAMPS Fuse and the fog lamp control 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

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

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

⇒	If the parameter does not change between the specified values, refer to Fog Lamp Switch Circuit Test.

2. Ignition ON, command the fog lamps ON and OFF with a scan tool. Observe the fog lamps turn on and off.

⇒	If the fog lamps do not turn on and off, refer to Fog Lamp Relay 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 an 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 Relay Circuit Test

1. Ignition OFF, disconnect the FOG LAMP relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the B+ circuit terminal 86 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the FOG LAMP relay.

4. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

5. Connect a test lamp between the B+ circuit terminal 86 and the control circuit terminal 85.
6. 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.

7. Connect a 15A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87.
8. Disconnect the harness connector at the appropriate fog lamp.
9. Verify that a test lamp illuminates between the fog lamp control circuit terminal A and ground.

⇒	If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance.

10. Verify that a test lamp illuminates between the fog lamp ground circuit terminal B and B+.

⇒	If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

11. If all circuits test normal, test or replace the FOG LAMP relay.

Front Fog Lamp Indicator Test

1. Ignition ON, with a scan tool perform the IPC Display Test. Verify the fog lamp indicator illuminates.

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

2. If all circuit test normal, replace the BCM.

Headlamp Switch

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Test for infinite resistance between the signal terminal 6 and the ground 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 between the signal terminal 6 and the ground 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.