GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2007 🢒 Corvette 🢒 Body Systems 🢒 Lighting 🢒 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 Relay Control

B2540 02

B2540 05

B2540 05

--

Rear Fog Lamp Voltage Supply

1

1

1

--

Rear Fog Lamp Switch Signal

2

2

2

--

Rear Fog Lamp Relay B+

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 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. For more detailed information concerning fog lamp operation refer to Exterior Lighting Systems Description and Operation .

Reference Information

Schematic Reference

Fog Lights Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

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

Scan Tool Reference

    •  Scan Tool Output Controls
    •  Scan Tool Data List
    •  Scan Tool Data Definitions

Circuit/System Verification

Ignition ON, observe the scan tool Rear Fog Lamp Switch parameter while pressing and releasing the rear fog lamp switch. The reading should toggle between ACTIVE and INACTIVE.

⇒If the reading does not change between the commanded states, refer to Rear Fog Lamp Switch Malfunction.

Circuit/System Testing

Rear Fog Lamp Switch Malfunction

  1. Ignition OFF, disconnect the C1 harness connector at the turn signal multifunction switch.
  2. Test for less than 1.0 ohm of resistance between the ground circuit terminal 3 and ground.
    3. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Rear Fog Lamp Switch parameter is INACTIVE.
    4. ⇒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.
    5. ⇒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 A6 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 relay switch B+ circuit terminal B4 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+ ignition circuit 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 A4 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. Test for less than 1.0 ohm of resistance between the inoperative rear fog lamp 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 rear fog lamp.
  8. Connect a 10A fused jumper wire between the B+ circuit terminal A4 and the relay controlled output circuit terminal B6. Verify the rear fog lamps are activated.
    9. ⇒If the rear fog lamps do not activate, test the relay controlled output circuit terminal B6 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.
    11. ⇒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.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Relay Replacement
    •  Turn Signal Multifunction Switch Replacement
    •  Control Module References for BCM replacement, setup, and programming