VATS (or Vehicle Anti-Theft System) can be associated with any vehicles Anti-Theft device, but it is commonly associated with the Anti-Theft devices of 1985 and newer GM vehicles.

The VATS system was first introduced on the Corvette in 1985, after proving successful, it was later introduced on other models in later years. There are several flavors of anti-theft device associated with the VATS system, most of which we won't cover here. Those include the PASSLOCK-I and II systems, which are located on vehicles 1995 and newer.

However, before this period were the PASSKEY-I and II systems, a simpler yet flawed design. The VATS system consists of a VATS decoder module located under the dash (above the Heater Core on a 91 Chevrolet Camaro) and two very light gauge wires that run from this module to the Ignition Lock Cylinder. The car key (typically separate keys for the door and the lock cylinder) contains a metal pellet surrounded by hard rubber. This pellet is impurified to specific levels to produce a designated resistance in the circuit.

The computer remembers this resistance in the key the very first time the key is inserted into the lock cylinder. From there forward, the computer will not allow the car to start without a key of similar resistance. Typically this procedure is done at the factory, on the assembly line.

PASSKEY-I:

There are 15 different combinations of resistance for each vehicle, the keys are randomly created and randomly assigned to different vehicles. When the wrong key is inserted into an already-programmed vehicle, the security light in the dash remains lit while the key is in the 'on' position. When removed, a counter starts which lasts between 2 to 4 minutes; during this period the vehicle cannot be started, even if you use the right key. In the PASSKEY-I system, the computer disables the starter relay box, so that the ignition system cannot supply voltage to the starter to start the car.
However, anyone with enough guts to climb under the car can start the car with a long screw driver; by crossing the posts on the starter.

GM found out people were doing this, the PASSKEY-I system was declared flawed, and the next generation, PASSKEY-II was put into active use.

PASSKEY-II:

The PASSKEY-II system has all the features of a PASSKEY-I system, it has the timer, the starter relay disable, and the 15 individual resistances.
The new thing in the PASSKEY-II system was an Injector Pulse disable. The computer sends a square wave pulse to the fuel injectors many times per second, to tell them when to mix fuel with the air. The PASSKEY-II system, when detecting the wrong key, disables this square wave pulse. Thus even if the starter was jumped off, the engine would not start (only crank) for lack of fuel.

THEFT:

Stealing a PASSKEY-II system enabled car can be hard, even the most experenced car thief could find themselves spending an hour trying every key resistance. Stealing a PASSKEY-I car isn't as hard, but both vehicles should come with a car alarm to begin with. The alarm (optional) and the factory standard VATS module has pretty much ensured that the car is not a hot item on the street.

VATS FLAWS:

As initially stated, the VATS system has two small-gauge wires that run to the lock cylinder. Because these wires are small gauge, and because they move WITH the cylinder, they tend to break. Average lifetime for a lock cylinder is 2 to 4 years, depending on how much the vehicle is driven.

Two things can happen from here.

1; The VATS system can be bypassed, allowing anyone with the right key (doesn't have to have the resistor) to start the car, but allows you to start your car. This method is not recommended.

2; You can take the car back to the dealer, where they'll cut you a new key for $45, and replace your lock cylinder for $297.

Overall, the PASSKEY-II system was a great idea, but there is that one major flaw, and the price is too much to have it fixed every 4 years or so.

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