For 1990-2009 cars

1. Ensure that the BCM is in the feature customization mode. Refer to On-Board Diagnostic Features .
2. Turn the ignition switch from the ACC position to the LOCK position then back to the ACC position within 1 second.

The BCM will enter the on-board diagnostic mode and flash the fasten seat belts indicator and sound the chime equal to the number of DTCs stored in the BCM memory. If no DTCs are stored, the BCM will not flash the fasten seat belts indicator or activate the chime.

The BCM flashes and sounds the first DTC with the lowest number, pauses, then continues with the next DTC until all of the DTCs are read. With a DTC 1, the BCM will only sound the chime once, and the fasten seat belts indicator will not flash. Once all of the DTCs are read, the BCM repeats this sequence 3 times.