All General Motors vehicles manufactured in 1993 equipped with a factory theft deterrence system, including all Cadillac models, use the same type of system, known as the Vehicle Anti Theft System (VATS). If the VATS detects that an attempted theft is in progress, four things will happen: The in-dash security warning light will come on, the VATS will disable the starter and the fuel injectors and the ignition key recognition module will not function for three minutes. The most common reason for the fault light to come on is inserting an incorrect key into the ignition. The keys contain a "key value," which the key recognition module checks. If the value is incorrect, the car will not start.
Check the key to ensure it is the correct one for the vehicle. If you insert a key with the improper key value, the key recognition system will not function and the car will not start. This is true even if you don't attempt to turn the ignition switch with the incorrect key. Since several General Motors keys will fit the ignition module, it is easy to make a mistake if you have other GM keys on you key chain.
Remove the incorrect key and wait three minutes. The in-dash security warning light should turn off, indicating that VATS has reset itself. If you now insert the correct key, the car should start as normal.
Attempt to start the car if the light doesn't turn off. If the car starts, this indicates that the car's Theft Deterrent Module (TDM) has detected a problem with the system. According to the 1993 Cadillac Seville's Owner's Manual, the TDM places the system into "fail-enable" mode and any key that fits the ignition and turns it will start the car. This allows you to drive the car in the case of a system malfunction instead of being stranded. A mechanic will need to check the car to troubleshoot and repair a problem with the system.
