Rear Fog Lamps Malfunction
Rear Fog Lamps Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
The rear fog lamp relay is supplied with battery voltage at all times. The rear fog lamp switch signal circuit is grounded momentarily by pressing the rear fog lamp switch. The instrument panel module (IPM) sends a GMLAN serial data message to the rear integration module (RIM) which 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, the relay switch contacts close and battery voltage is applied through the REAR FOG LAMP fuse to the rear fog lamp supply voltage circuit which illuminates the rear fog lamps.
Reference Information
Schematic Reference
Fog Lights Schematics (Fog Lights Schematics)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Exterior Lighting Systems Description and Operation (Exterior Lighting Systems Description and Operation)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (Programming and Relearning)
Circuit/System Verification
Ignition ON, with a scan tool, command the rear fog lamps ON and OFF. The rear fog lamps should turn ON and OFF when commanded.
If the rear fog lamps turn ON and OFF when commanded, refer to Rear Fog Lamp Switch Malfunction.
Circuit/System Testing
Rear Fog Lamp Switch Malfunction
1. Ignition OFF, disconnect the 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 that a test lamp does not illuminate between B+ and the rear fog lamp switch signal circuit terminal 2.
• If the test lamp illuminates, test the signal circuit for a short to ground. If the circuit tests normal, replace the IPM.
4. Install a 3-A fused jumper wire between the signal circuit terminal 2 and the ground circuit terminal 3. Verify the rear fog lamps are ON.
• If the rear fog lamps are OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the IPM.
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 R35 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 R32 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 terminal R32 for a short to ground. If the circuit tests normal, test or replace the rear fog lamp relay.
4. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal R31 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, scan tool OFF, exterior lamps OFF, test for less than 5.0 ohms between the inoperative rear fog lamp ground circuit 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 15-A fused jumper wire between the B+ circuit terminal R32 and the relay controlled output circuit terminal R33. Verify the rear fog lamps are activated.
• If the rear fog lamps do not activate, test the relay controlled output circuit terminal R33 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 R31 and the control circuit terminal R35
10. Command the rear fog lamps ON and OFF with the 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 RIM.
• If the test lamp is always OFF, test the control circuit for a short to voltage or open/high resistance. If the circuit tests normal, replace the RIM.
11. If all circuits test normal, test or replace the rear fog lamp relay.
Rear Fog Lamp Indicator Malfunction
Ignition ON, with a scan tool perform the display test for the instrument panel cluster (IPC) and observe the rear fog lamp indicator.
If the rear fog lamp indicator does not illuminate during the test or remains illuminated at all times, replace the IPC.
If the rear fog lamp indicator illuminates during the test, replace the IPM.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Underhood Electrical Center or Junction Block Replacement (Service and Repair)
* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))
* Turn Signal Multifunction Switch Replacement (Turn Signal Multifunction Switch Replacement)
* Control Module References (Programming and Relearning) for IPM, IPC, or RIM replacement, setup, and programming