The rear fog lamp switch signal circuit is grounded momentarily by pressing the rear fog lamp switch. The body control module (BCM) energizes the rear fog lamp relay by applying ground to the rear fog lamp relay control circuit. When the rear fog lamp relay is energized, battery voltage is applied via the REAR FOG/ALDL TOP SW fuse to the rear fog lamp supply voltage circuit which illuminates the rear fog lamps.

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

Ignition ON, observe the scan tool Rear Fog Lamp Switch parameter while pressing and releasing the rear fog lamp switch. The parameter should change between Active and Inactive.

Rear Fog Lamp Switch Malfunction

1. Ignition OFF, disconnect the X1 harness connector at the turn signal/multifunction switch.
2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal 3.

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

3. Ignition ON, verify the scan tool Rear Fog Lamp Switch parameter is Inactive.

⇒	If not the specified value, test the signal circuit terminal 2 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 2 and the ground circuit terminal 3. Verify the scan tool Rear Fog Lamp Switch parameter is Active.

⇒	If not the specified value, test the signal circuit terminal 2 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 turn signal/multifunction switch.

Rear Fog Lamps Malfunction

1. Ignition OFF, disconnect the rear fog lamp relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal B6 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 relay switch B+ circuit terminal A4 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+ fuse is open, test the control circuit terminal B6 for a short to ground. If the circuit tests normal, test or replace the rear fog lamp relay.

4. Verify that a test lamp illuminates between the B+ circuit terminal B4 and ground.

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

5. Disconnect the harness connector at the inoperative rear fog lamp.
6. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the inoperative rear fog lamp ground circuit terminal 1 and ground

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

7. Connect the harness connector at the inoperative rear fog lamp.
8. Connect a 10A fused jumper wire between the B+ circuit terminal A4 and the control circuit terminal B6. Verify the rear fog lamps are illuminated.

⇒	If the rear fog lamps do not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the inoperative rear fog lamp.

9. Connect a test lamp between the B+ circuit terminal B4 and the control circuit terminal A6.
10. Command the Rear 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.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.