VATS (Vehicle Anti Theft System) was introduced by GM on the 1986 Corvette because the Corvette had become the number one target of car thieves. Corvette thefts dropped so impressively after VATS was implemented that GM expanded the system in 1988 to the Camaro , Firebird, and Cadillac Seville...
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In the beginning, all interrogators had to connect to the wiring under the dash. The VATS wire can usually be found easily under the dash after removing the knee bolster. Once the wire has been located, the wire from the interrogator is connected to matching connectors on the VATS wire. Some interrogators only have one connector and it is attached to the wire that leads away from the steering column. The connectors will only fit one way so there is no danger of connecting the interrogator to the wrong wire. Connecting under the dash is the most reliable way to connect your interrogator because it eliminates any potential problems in the wiring to the lock and in the lock itself. If a vehicle starts when the interrogator is connected under the dash but not when the key is used in the ignition, that usually indicates wiring to the keyway is damaged and the lock needs to be replaced.
In 1990, GM changed the wiring on some of the VATS vehicles, particularly on the Cadillacs , so that it went to the large “bulkhead connector” as shown in Photo 3, that all of the other steering column wiring runs through. A large bulky adaptor is required in order to connect to these vehicles under the dash. The bulkhead connector became known as the “48-pin connector” by locksmiths, and the adaptor is usually called a 48-pin adaptor. Using the 48-pin adaptor is awkward at best, which is why several different companies have introduced systems to connect through the ignition lock rather than below the dash.
The systems that connect through the ignition lock fall into two types – ones that use disposable plastic keys and ones that fit over the head of the mechanical key. Photo 4 shows a typical plastic key and Photo 5 shows the TT4002 VATS ByPass adaptor. The plastic keys can only be used once because they have to be cut to fit the vehicle. Care should always be used when cutting a plastic key to make sure that all burrs have been removed so that they do not come off and jam the ignition. Because the plastic keys are actual keys, different keys are required for the single-sided system and the double-sided system.
The TT4002 VATS ByPass adaptor has a boot that will fit over the head of either a single-sided key or a double-sided key. Once the boot is in place, the key and the adaptor are inserted into the ignition lock. The connector on the other end of the ByPass adaptor is identical to the connector found under the dash, so any interrogator will plug into the ByPass adaptor. Once the ByPass adaptor is connected to the interrogator and the key is turned in the ignition, the interrogation can begin. The advantage of the TT4002 VATS ByPass adaptor is that it is reusable and that will work on both single-sided and double-sided systems.
How does an interrogator work?
The original VATS interrogator was manufactured by Kent-Moore, which at the time manufactured most of GM's special tools. Since these tools were not readily available to locksmiths, other manufacturers developed and marketed similar tools to accomplish the same job. My favorite interrogator, the Tech-Train 4004A, is shown in Photo 6. All interrogators, regardless of who manufactures them, include a selector switch that will allow you to pass the electrical current from the car through any one of the 15 resistor values. When properly connected to the car, the electrical current that would normally flow through the key is re-directed to the interrogator's built-in resistors and then flows back to the computer in the car. The interrogator acts as the resistor pellet in the key so that when the proper value is selected the car will start and run.
The process of interrogation is simply attempting to start the vehicle with one resistor value after the other until the vehicle starts, pausing between each value for the duration of the time delay. Some interrogators have a built-in timer that signals you when four minutes have elapsed. I never use one of these timers (the TT-4004A doesn't have a timer) because I know that there has never been a vehicle built with a four-minute delay. In the original information sent to the dealers it is clearly stated that the time delay is “two minutes plus.” In my research, I've proven that a three-minute wait is all that is necessary on any VATS system except for the one used on the 1990 Corvette – more on that later. It appears to me that the original interrogator, which was designed for use by Chevrolet mechanics, who charge by the hour, had a four-minute timer because four-minute timers were probably available at a reduced price. Other manufacturers probably followed suit just because the original unit had a four-minute timer.
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