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 Descriptors
DTC B2540 02: Rear Fog Lamps Control Circuit Short to GroundDTC B2540 05: Rear Fog Lamps Control Circuit Open or Short to Voltage
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Rear Fog Lamp Relay B+ | 1 | 1 | -- | -- |
Rear Fog Lamp Switch Signal | 1 | 1 | -- | -- |
Rear Fog Lamp Relay Control | B2540 02 | B2540 05 | B2540 05 | -- |
Rear Fog Lamp Control | 1 | 1 | 1 | -- |
Rear Fog Lamp Relay Ground | -- | 1 | 1 | -- |
Fog Lamp - LR Ground | -- | 1 | 1 | -- |
Fog Lamp - RR Ground | -- | 1 | 1 | -- |
Fog Lamp Switch Ground | -- | 1 | 1 | -- |
1. Rear Fog Lamps 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 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.
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. |
| • | A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred. |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Testing
- Ignition OFF, disconnect the rear fog lamp relay.
- Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal B1 and ground.
- Connect a test lamp between the control circuit terminal B2 and ground.
- 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 all circuits test normal, test or replace the rear fog lamp relay.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | 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. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure
| • | Control Module References for BCM replacement, setup, and programming |
