VATS (Vehicle Anti-Theft System) is the original GM starter interrupt anti-theft system. Characterized by the resistor found in the blade of the ignition key, VATS was used on many GM makes and models from the mid 1980s through the early 2000s.
History of the GM VATS
We started to see VATS-equipped vehicles beginning in the 1980s. The systems are easily identified by the "resistor" mounted in the metal blade of the ignition key. There are fifteen different resistor values available. In order for the engine to start, the correct "resistor" must be read by the VATS control module via the ignition lock cylinder. The ignition lock cylinder must also be rotated to the "crank" position. If the incorrect code is read, the system will not allow the engine to start for four minutes, even if the correct code is received after. The security light will remain on or a message will be displayed on the Driver Information Center (depending on the model) when this occurs.
What the Warning Light Means
It is normal for the warning light to be on during bulb check and off when the engine is running, with no message displayed on the Driver Information Center (DIC). When the system detects a fault, the warning light will illuminate or a message will be displayed on the DIC, depending on the model. If a fault occurs while driving, the engine may or may not start after turning the ignition off. If a fault occurs when trying to start the vehicle, the vehicle probably won't start.
By far the most common problem with the VATS system is broken wires in the steering column that connect the ignition lock cylinder to the under-dash wire harness. The proper repair is to replace the ignition lock cylinder, which comes with the wires that snake down the steering column already attached. The new lock cylinder will come with a blank key that will only rotate the new lock cylinder—it does not have a resistor in it that will actually start the car. A new key must be made from the blank, which now has the proper resistor value. (Normally the resistor is read from the old key using a tool called an interrogator. The interrogator is available in the parts department of most GM dealers.)
There is no relearn procedure for the VATS system unless the VATS control module is replaced. A new VATS module will learn the resistor code the first time it is powered up in the car. Once the module learns its code, there is no way to re-learn it. New ignition keys must always be matched to the learned code in the VATS control module. If all keys are lost and the VATS code is unknown, then trial and error must be used to find the correct VATS code, though, in some cases, the VATS code may be available from your local General Motors parts department.