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DTC B2740

DTC B2740

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.


DTC Descriptor

DTC B2740 00

Front Fog Lamp Switch Circuit Malfunction

Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performance
Lighting Control Switch Reference B1405 03, B1529 03, B2740 00 B257B 03 1 -
Lighting Control Switch Signal B257B 03 B257B 03 1 -
1. Front Fog 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 body control module (BCM) 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 front fog lamp fuse to the front fog lamp supply voltage circuit which illuminates the front fog lamps.

Conditions for Running the DTC


• The ignition is turned ON.

• Front fog lamp switch activated.


Conditions for Setting the DTC

The BCM detects the fog lamp switch is continuously active.

Action Taken When the DTC Sets

Front fog lamps will be continuously illuminated.

Conditions for Clearing the DTC


• The DTC will be current for as long as the fault is present.

• When the fault is no longer present, the DTC will be a history DTC.

• A history DTC will clear after 50 ignition cycles.


Conditions for Clearing the DTC

The condition for setting the DTC is not longer present.

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. Observe the scan tool front fog lamps switch parameter while turning the front fog lamps switch ON and OFF. The parameter should change between Active and Inactive.

Circuit/System Testing


1. Ignition OFF, disconnect the harness connector at the S30 headlamp switch.

2. Ignition ON, test for greater than 10V between the 12 V reference circuit terminal 1 and ground.

3. If less than the specified range, test the 12 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 BCM.

4. Test for 0.4K Ω to 1K Ω between the signal circuit terminal 12 and ground.

5. If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 BCM.

6. If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the K9 BCM.

7. If all circuits test normal, test or replace the S30 headlamp switch.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Headlamp Switch Replacement

• Control Module References for BCM replacement, setup, and programming