* Incorrect Key: This is the most common cause. The car won't start or will show a theft-deterrent light. Solution: Try a different key known to work. If you only have one key, you'll need a replacement from a locksmith or dealership that can program a new key to match your car's system.
* Low Battery: A weak battery can sometimes trigger the anti-theft system. Solution: Jump start the car from another vehicle's battery. If the problem persists after a good jump start, the battery might need replacing.
* Faulty Passlock System (if equipped): The 1989 DeVille might have a Passlock system (a basic electronic immobilizer). If the Passlock module malfunctions, it can prevent the car from starting, even with the correct key. Solution: This requires professional diagnosis and potentially replacement of the Passlock module.
* Aftermarket Alarm System: If a previous owner installed an aftermarket alarm system, that system might be malfunctioning and triggering the anti-theft features. Solution: Locate the alarm system's control module and consult its manual for troubleshooting and reset procedures. This often involves disconnecting the battery for a short time.
Important Steps Before Doing Anything:
1. Consult your owner's manual: While it might be old, the manual should contain some information about the anti-theft system and possible troubleshooting steps.
2. Check the obvious: Ensure the steering wheel isn't locked, the gear shifter is in park (or neutral), and that your lights aren't left on (draining the battery).
If you suspect a more serious issue with the anti-theft system, avoid repeatedly attempting to start the car. This could damage the electrical system. It's best to seek professional help from an automotive locksmith or a mechanic experienced with older Cadillacs. They possess the diagnostic tools to identify the root cause of the problem and provide a safe and effective solution.
