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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2008 🢒 STS 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Front Fog Lamps Malfunction

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Front Fog Lamp Switch Signal

2

2

2

--

Front Fog Lamp Relay Control

1

1

1

--

Front Fog Lamps Control

1

1

1

--

Fog Lamp - LF Ground

--

1

1

--

Fog Lamp - RF Ground

--

1

1

--

Fog Lamp Switch Ground

--

2

2

--

1. Front Fog Lamps Malfunction

2. Front Fog Lamp Switch Malfunction

Circuit/System Description

The front fog lamp relay is supplied with battery voltage at all times. The front fog lamp switch signal circuit is grounded momentarily by pressing the front fog lamp switch. The instrument panel module (IPM) energizes the front fog lamp relay by applying ground to the front fog lamp relay control circuit. When the front fog lamp relay is energized, the relay switch contacts close and battery voltage is applied through the FOG LAMP fuse to the front fog lamp supply voltage circuit which illuminates the front fog lamps.

Reference Information

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

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, with a scan tool, command the Front Fog Lamps On and Off. The front fog lamps should turn ON and OFF when commanded.

⇒If the front fog lamps turn ON and OFF when commanded, refer to Front Fog Lamp Switch Malfunction.

Circuit/System Testing

Front 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.
    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 signal circuit terminal 4.
    4. ⇒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 4 and the ground circuit terminal 3. Verify the front fog lamps are illuminated.
    5. ⇒If the front fog lamps do not illuminate, 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.

Front Fog Lamps Malfunction

  1. Ignition OFF, disconnect the front fog lamp relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal R4 and ground.
    3. ⇒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 R2 and ground.
    4. ⇒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 R3 for a short to ground. If the circuit tests normal, test or replace the front fog lamp relay.
  4. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal R1 and ground.
    5. ⇒If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  5. Disconnect the harness connector at the inoperative front fog lamp.
  6. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal 1 and ground.
    7. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the harness connector at the inoperative front fog lamp.
  8. Connect a 15-A fused jumper wire between the B+ circuit terminal R2 and the control circuit terminal R3. Verify the front fog lamps are activated.
    9. ⇒If the front fog lamps do not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the inoperative front fog lamp.
  9. Connect a test lamp between the B+ circuit terminal R1 and the control circuit terminal R4
  10. Command the Front Fog Lamps ON and OFF with the scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    11. ⇒If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the IPM.
    ⇒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 IPM.
  11. If all circuits test normal, test or replace the front fog lamp relay.

Front Fog Lamp Indicator Malfunction

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

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Front Fog Lamp Bulb Replacement
    •  Underhood Electrical Center or Junction Block Replacement
    •  Relay Replacement
    •  Turn Signal Multifunction Switch Replacement
    •  Control Module References for IPM or IPC replacement, setup, and programming