B2540

DTC B2540

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

DTC DESCRIPTORS

DTC B2540 02
Rear Fog Lamps Control Circuit Short to Ground

DTC B2540 05
Rear Fog Lamps Control Circuit Open or Short to Voltage




DIAGNOSTIC FAULT INFORMATION

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 battery voltage 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.

CONDITIONS FOR RUNNING THE DTC
Battery voltage must be between 9-16 volts.

CONDITIONS FOR SETTING THE DTC

B2540 02
This DTC will set when the BCM detects a short to ground in the rear fog lamp relay control circuit.

B2540 05
This DTC will set when the BCM detects an open or short to voltage in the rear fog lamp relay control circuit.

ACTIONS TAKEN WHEN THE DTC SETS
- When DTC B2540 02 is present, the rear fog lamps will not operate when the park lamps are ON and the rear fog lamp switch is active.
- When DTC B2540 05 is present, the rear fog lamps and/or the rear fog lamp indicator will be ON at all times or will not operate.

CONDITIONS FOR CLEARING THE DTC
- The condition responsible for setting the DTC no longer exists.
- You issue a scan tool CLEAR DTCs command.
- A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

CIRCUIT/SYSTEM TESTING
1. Ignition OFF, disconnect the rear fog lamp relay.
2. Test for less than 1 ohm of resistance between the ground circuit terminal B1 and ground.
- If greater than the specified range, test the ground circuit for an open/high resistance.
3. Connect a test lamp between the rear fog lamp relay control circuit terminal B2 and the ground circuit terminal B1.
4. Command the rear fog lamps ON and OFF with the rear fog lamp switch. The test lamp should turn ON and OFF when changing between the commanded states.
- If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
- If the test lamp is always OFF, test the control circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the BCM.
5. 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 Verification Tests

- Relay Replacement (Attached to Wire Harness) Relay Replacement (Within an Electrical Center)
- Control Module References for BCM replacement, setup, and programming. Programming and Relearning