What you might be thinking of is:
* Clearing trouble codes: If you're having problems and want to clear diagnostic trouble codes (DTCs), you'll need to use a scan tool (OBD-I, not OBD-II, as it's an older vehicle) to read and clear the codes. A mechanic would have the proper equipment. You can't just reset them by disconnecting the battery.
* Resetting the computer (indirectly): Disconnecting the negative (-) terminal of the battery for about 30 minutes (or longer) will often clear some of the ECM's short-term memory. This might help resolve minor glitches, but it won't erase the car's programming or fix major problems. Remember to reconnect the battery correctly after this time or you may trigger the theft-deterrent system in some vehicles.
* Dealing with a specific problem: If you're experiencing a particular issue (e.g., a malfunctioning gauge, intermittent starting problem), a "reset" isn't the solution. You'll need to diagnose the underlying cause, which may require professional help.
In summary, there's no single "reset" button or procedure. The best approach depends entirely on the problem you're facing. If you have a specific issue with your 1991 Cadillac DeVille, providing more detail will help pinpoint the appropriate steps.
