GM Anti Theft System Usage

When diagnosing a no start condition these days, it's always a good idea to consider if the vehicle has a theft deterrent system that could be the cause. There's nothing more frustrating than chasing, say, a no crank, or a start and stall, only to find that the system is "only doing its job"! On many older vehicles, you can only check with the owner to see what, if any, after-market " alarm" may have been added. Car companies have increasingly made their own systems available either as options or standard equipment.
Since the mid 80's GM has used a variety of anti-theft systems, starting with the high end '86 Corvette, working on down to most of their carlines today. Listed below is a breakdown of factory installed systems you can expect to find in GM cars since the '80s. Also noted are what the system disables along with any relearn the system uses. Note that this article covers what GM calls "VTD" or vehicle theft deterrent systems. These systems prevent the vehicle from being driven. Content Theft Deterrent protects against break in, and will not be covered here. Why is it important for you to know which system (if any) the car uses? Here's an example: you have a '96 Cavalier with a no crank situation. The "THEFT" light is illuminated on the dashboard. After checking the list, it turns out that the Passlock system used on this car does not affect cranking. Now you can chase the starter circuit problem without second-guessing.

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