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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

B257B 03

B257B 03

B257B 07

-

Front Fog Lamp Relay Control

B2530 02

B2530 04

B2520 01

--

Right Front Fog Lamp Control

1

3

2

--

Left Front Fog Lamp Control

1

4

2

--

Right Front Fog Lamp Ground

--

3

--

--

Left Front Fog Lamp Ground

--

4

--

--

1. Front Fog Lamps Inoperative

2. Front Fog Lamps Always ON

3. Right Front Fog Lamp Inoperative

4. Left Front Fog Lamp Inoperative

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 body control module (BCM) energises the front fog lamp relay by applying ground to the front fog lamp relay control circuit. When the front fog lamp relay is energised, the relay switch contacts close and battery voltage is applied through the front fog lamp fuse to the front fog lamp supply voltage circuit which illuminates the front fog lamps.

Reference Information

Schematic Reference

Fog Lamps 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

  1. Ignition ON, observe the scan tool Front Fog Lamps Switch parameter. The parameter should change between Active and Inactive each time the front fog lamp switch is pressed.
  2. If the parameter does not change, refer to Fog Lamp Switch Malfunction
  3. Command the Fog Lamps ON and OFF with a scan tool. The front fog lamps should turn ON and OFF when changing between the commanded states.
  4. If the fog lamps are always ON or always OFF, refer to Front Fog Lamps Malfunction

Circuit/System Testing

Fog Lamp Switch Malfunction

  1. Ignition OFF, disconnect the X1 and X3 harness connectors at the K9 Body Control Module.
  2. Ignition ON, test for less than 0.3 V between the signal circuit terminal 9 X1 and ground.
  3. If greater than the specified value, test the circuits listed below for a short to voltage. If the circuit tests normal, replace the S30 Headlamp Switch.
    • Signal circuit terminal 9 X1
    • 12 V reference voltage circuit terminal 4 X3
  4. Ignition OFF, test for infinite resistance between the signal circuit terminal 9 X1 and ground.
  5. If less than infinite resistance, test the circuits listed below for a short to ground. If the circuit tests normal, replace the S30 Headlamp Switch.
    • Signal circuit terminal 9 X1
    • 12 V reference voltage circuit terminal 4 X3
  6. Test for 7.4-7.9 kΩ between the signal circuit terminal 9 X1 and the 12 V reference voltage circuit terminal 4 X3.
  7. If less than 7.4 kΩ, test the signal circuit and the 12 V reference circuit for a short circuit. If the circuit tests normal, replace the S30 Headlamp Switch.
    If greater than 7.9 kΩ, test the signal circuit and the 12 V reference circuit for an open/high resistance. If the circuit tests normal, replace the S30 Headlamp Switch.
  8. Test for 2.7-3.1 kΩ between the signal circuit terminal 9 X1 and the 12 V reference voltage circuit terminal 4 X3 while pressing the front fog lamp switch.
  9. If not the specified range, replace the S30 Headlamp Switch.
  10. If all circuits test normal, replace the K9 Body Control Module.

Front Fog Lamps Malfunction

  1. Ignition OFF, disconnect the appropriate harness connector at the front fog lamps listed below:
  2. • E29LF Fog Lamp - Left Front
    • E29RF Fog Lamp - Right Front
  3. Test for less than 5 Ω between the appropriate front fog lamp ground circuit harness connector terminal A and ground.
  4. If greater than the specified value, test the ground circuit for an open/high resistance.
  5. Remove the F48UA fuse. Verify that the front fog lamps do not illuminate.
  6. If any front fog lamp does illuminate, test the signal circuit for a short to voltage.
  7. Install a 10 A fused jumper wire between the fuse output contact and B+. Verify that the front fog lamps illuminate.
  8. If the front fog lamps do not illuminate, test the signal circuit terminal for a short to ground or an open/high resistance. If the circuit tests normal, replace the appropriate front fog lamp.
  9. Disconnect the X2 harness connector at the X50A Fuse Block - Underhood.
  10. Connect a test lamp between the signal circuit terminal 19 X2 and B+.
  11. Ignition ON, perform the Front Fog Lamps test. The test lamp should turn ON and OFF when changing between the commanded states.
  12. If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit tests normal, replace the K9 Body Control Module.
    If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 Body Control Module.
  13. If all circuit test normal, replace the X50A Fuse Block - Underhood.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Headlamp Switch Replacement
    •  Front Fog Lamp Bulb Replacement
    •  Front Compartment Fuse Block Replacement
    • Control Module References for BCM replacement, setup and programming
   


© Copyright Chevrolet. All rights reserved
   


© Copyright Chevrolet. All rights reserved