VATS stands for Vehicle Anti-theft System and is also known as PASS-Key (Personal Automotive Security System). Each VATS key has a resistor embedded within the key-blade, and each resistor has 1 of 15 possible values. Sometimes the resistors are refered to as a Vats Pellet or Vats Chip. Decoding a VATS key is very simple, but it requires that you know how to use an ohm meter. Any multimeter will have an ohm meter and any Radio Shack, Electronic or Hardware Store can sell you one.
All VATS keys have a resistor embedded in the key blade with metal prongs protruding out of each side of the key blade. In order to read the resistance of the resistor in the key blade, place one lead of the ohm meter on one metal prong, and the other lead on the other metal prong, opposite, on the other side of the key blade. With the leads in their proper position a resistance value can be read from the ohm meter.
Go to a Radioshack or other electronics equipment store and use a Digital Multimeter.
Switch it to measure Kilo-Ohms (resistance.)
Take the ends of the terminals of the tester and place them on the metal thread at the center of the VATS chip.
Measure the Kilo-Ohms. It will be between 0 and 12.
Use this chart to decide which VATS key chip # you need. Round your number to the nearest value on the chart to determine which VATS chip number your key has.
VATS Chip Number