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Makes 🢒 Cadillac 🢒 2008 🢒 STS 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Rear 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

Rear Fog Lamp Switch Signal

2

2

2

--

Rear Fog Lamp Relay Control

1

1

1

--

Rear Fog Lamp Control

1

1

1

--

Fog Lamp - LR Ground

--

1

1

--

Fog Lamp - RR Ground

--

1

1

--

Fog Lamp Switch Ground

--

2

2

--

1. Rear Fog Lamps Malfunction

2. Rear Fog Lamp Switch Malfunction

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 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

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 Rear FogLamps 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.
    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 2.
    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 2 and the ground circuit terminal 3. Verify the rear fog lamps are illuminated.
    5. ⇒If the rear 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.

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.
    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 R32 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 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.
    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 rear fog lamp.
  6. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal B 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 rear fog lamp.
  8. Connect a 15-A fused jumper wire between the B+ circuit terminal R32 and the control circuit terminal R33. Verify the rear fog lamps are activated.
    9. ⇒If the rear fog lamps do not activate, test the control 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.
    11. ⇒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 illuminates during the test, replace the IPM.
⇒If the rear 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.

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