Test Description

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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. Depress the switch for both the ON and OFF states. Repeat as necessary.
3. Tests for voltage at the coil side of the rear fog lamp relay.
4. Verifies that the body control module (BCM) is providing ground to the rear fog lamp relay.
5. Tests if ground is constantly being applied to the rear fog lamp relay.
6. 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.

Fig 1: DTC B2540 Diagnostic Procedure (Step 1 To 6)

Courtesy of GENERAL MOTORS CORP.

Fig 2: DTC B2540 Diagnostic Procedure (Step 7 To 13)

Courtesy of GENERAL MOTORS CORP.