B2540

DTC B2540

CIRCUIT DESCRIPTION
When the body control module (BCM) senses that the rear fog lamp switch signal circuit is grounded momentarily by pressing the rear fog lamp switch, the BCM energizes the rear fog lamp relay by grounding the rear fog lamp relay control circuit. The rear fog lamp indicator is also illuminated utilizing the same fog lamp relay control circuit.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:

DTC B2540 Rear Fog Lamps Control Circuit

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

CONDITIONS FOR SETTING THE DTC
- When the BCM receives a rear fog lamp switch OFF command and the rear fog lamp relay control circuit is shorted to ground.
- When the BCM receives a rear fog lamp switch ON command and the rear fog lamp relay control circuit is shorted to voltage or open.

ACTION TAKEN WHEN THE DTC SETS
The rear fog lamps will not operate or will remain always on.

CONDITIONS FOR CLEARING THE MIL/DTC
- This DTC will clear on current status after the condition for setting the fault is corrected.
- A history DTC will clear after 100 consecutive ignition cycles without a fault present.
- History and current DTCs can be cleared using a scan tool.

TEST DESCRIPTION

Step 1 - Step 13:

The numbers below refer to the step numbers on the diagnostic table.
2. Listen for an audible click when the rear fog lamp relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
3. This step tests for voltage at the coil side of the rear fog lamp relay.
4. This step verifies that the BCM is providing ground to the rear fog lamp relay.
5. This step tests if ground is constantly being applied to the rear fog lamp relay.
6. This step tests if there is opposing voltage present or an open in the rear fog lamp relay control circuit.
12. After replacement of the BCM you must calibrate the new module for proper operation.