Resistor  Value Code  Ohms Value
1               N/A                0.402
2               CN                 0.523
3               FW                 0.681
4               GP                 0.887
5               KA                 1.130
6               N5                 1.470
7               UN                1.870
8               XB                 2.370
9               GA                 3.010
10             NP                 3.740
11             FY                  4.750
12             C5                  6.040
13             XY                  7.500
14             KB                 9.530
15             UW               11.800
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.

Before long, VATS was standard equipment on all Cadillac vehicles and on many other Chevrolet, Pontiac, Buick, and Oldsmobile vehicles.

As the system was added to more vehicles, GM began using the terms “PASSkey-1” and “PASSkey-2” as more descriptive names for the system. 

From the locksmith’s point of view, there is no functional difference between VATS and PASSkey-1 or PASSkey-2, and most technicians still refer to the system simply as VATS 
The system itself operates on a very simple principal. 
In addition to the standard side-bar ignition, there is a resistor embedded into the key. 
When the key is inserted into the lock and turned, an electrical current runs through the resistor. 
The amount of current drop caused by the resistor is measured by a computer. 
If the current drop matches the pre-set value stored in memory, the car is allowed to start. 
If the current drop is higher or lower than the pre-set value, the vehicle will be prevented from starting – even with the correct key – for several minutes. 
No alarm sounds and the only indication that the vehicle has been disabled is an indicator on the dash.
The time delay feature was the main reason that VATS proved so successful. 
Studies showed that if a would-be car thief could be slowed down, even for a few minutes, they would look for an easier target. 
VATS equipped vehicles soon became some of the least stolen vehicles on the road. 
The insurance companies went from charging a surcharge for owing a Corvette to offering a discount on the Corvette or any other vehicle that was equipped with the VATS system