Front Fog Lamps Malfunction
Front Fog Lamps Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
The fog lamp relay is supplied with battery voltage at all times. The fog lamp switch signal circuit is grounded momentarily by pressing the fog lamp switch. The body control module (BCM) energizes the fog lamp relay by applying ground to the fog lamp relay control circuit. When the fog lamp relay is energized, the relay switch contacts close and battery voltage is applied through the FOG LAMP fuse to the fog lamp supply voltage circuit which illuminates the fog lamps.
Reference Information
Schematic Reference
Fog Lights Schematics Fog Lights Schematics
Connector End View Reference
Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)
Description and Operation
Exterior Lighting Systems Description and Operation Exterior Lighting Systems
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References for scan tool information
Circuit/System Verification
1. Ignition ON, observe the scan tool Front Fog Lamp Switch parameter while activating the front fog lamp switch. The parameter should change between Active and Inactive.
• If the parameter does not change between the selected states, refer to Fog Lamp Switch Malfunction.
2. Turn the front fog lamps ON and OFF with the front fog lamps switch. The front fog lamps should turn ON and OFF as selected.
• If the front fog lamps do not change between the selected states, refer to Fog Lamps Malfunction.
3. Command the Lamp Test ON and OFF with a scan tool. The front fog lamps indicator should turn ON and OFF when changing between the commanded states.
• If the front fog lamps indicator illuminates during the test, replace the BCM.
• If the front fog lamps indicator does not illuminate during the test or remains illuminated at all times, replace the instrument cluster.
Circuit/System Testing
Fog Lamp Switch Malfunction
1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
2. Verify that a test lamp illuminates between B+ and the ground circuit terminal 8.
• 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 10 for a short to ground. If the circuit tests normal, replace the BCM.
4. Install a 3 A fused jumper wire between the signal circuit terminal 10 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 and panel dimmer switch.
Fog Lamps Malfunction
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 30 and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
4. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.
• If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
5. Ignition OFF, disconnect the harness connector at the appropriate fog lamp.
6. Test for less than 5.0 ohms between the ground circuit terminal B and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
7. Connect the harness connector at the fog lamp.
8. Connect a 15 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the fog lamps are activated.
• If the fog lamps do not activate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the fog lamp.
9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
10. 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.
11. If all circuits test normal, test or replace the fog lamp relay.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Fog Lamp Switch Replacement (with RPO SLT) Fog Lamp Switch Replacement (with RPO SLT)Fog Lamp Switch Replacement (without RPO SLT) Fog Lamp Switch Replacement (without RPO SLT)
* Front Fog Lamp Replacement (Chevrolet) Removal and ReplacementFront Fog Lamp Replacement (GMC) Removal and Replacement
* Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)
* Headlamp Switch Replacement (without RPO SLT) Headlamp Switch Replacement (without RPO SLT)Headlamp Switch Replacement (with RPO SLT) Headlamp Switch Replacement (with RPO SLT)
* Control Module References Control Module References for BCM replacement, setup, and programming