VAT Key Codes and Values

Someone posted
this a while back in C4 tech.
Corvette VATS Key Codes and
Associated resistance Codes in OHMS
Pellet Resistance
Code Ohms
1 – 402
2 – 523
3 – 681
4 – 887
5 – 1130
6 –
1470
7 – 1870
8 – 2370
9 – 3010
10 – 3740
11 – 4570
12 –
6040
13 – 7500
14 – 9530
15 – 11800
VATS, these four
letters can instill fear in even the most stalwart of Corvetters.
The Vehicle Anti-Theft System was introduced to the Corvette for
Model Year 1986 and has been a thorn in the side of many 1986 – 1988
Corvette owner. At this point a discussion of the system is in order as
there are many misconceptions concerning this system.
VATS
SYSTEM
The key (pardon the pun) to the system is the special ignition
key that contains the resistor pellet, this pellet connects to the VATS
module which allows it to:
1. Signal the ECM.
2. Close the starter
circuit.
Without a signal response from the VATS module, the ECM
will not allow fuel injection or starter operation.
VATS is not
connected to the alarm system, so it is active even if the alarm system is
defeated, or if the car is left unlocked.
The two main components
of the system are the ignition key with resistor pellet and the VATS
decoder module. The pellet in the key is just a resistor, it will be one
of 15 specific values. The ignition cylinder has contacts that connect
between the two sides of the ignition key pellet. Wiring carries this
resistance value to the VATS decoder module, where it is compared to the
value stored in the module. If they match, the car starts. If they do not
match, the starter circuit and fuel injectors are disabled. A timer
(approximately 4 minutes) is also activated if an improper resistance is
read. Each time an attempt is made during this delay period, the timer
will be reset. So it is important to wait at least 4 minutes before
another attempt is made.
The main problem with the system in the
first three years of production was the material that the contacts of both
the ignition key and ignition cylinder were made of. This material was
prone to premature wear, causing poor contact, an incorrect resistance
being seen by the decoder module and a no start condition. This caused
embarrassment when your shiny Corvette wouldn’t start and your
significant other laughs uncontrollably and offers to drive you in her
Civic. It also causes inconvenience and more embarrassment when you need
to call the AAA for a tow.
Band-aides were developed that would
fool the decoder module. These Band-aides bypassed the key pellet and the
ignition cylinder contacts. The VATS Bypass Modules that you see in the
Corvette catalogs cost anywhere from $30 – $50. Add to that shipping and
sales tax where applicable and you�re looking at $35 for a resistor that
you can pick up at Radio Shack for under $1! Another problem with the
bypass modules is that you have to know what code value (1-15) to buy.
That means you’ll have to go to a dealer that can use their VATS
Interrogator.
If you take a multi-meter and measure the resistance
between the metal contacts on either side of your key, you can buy a
resistor of this value at any Radio Shack store. � watt will do. You then
need to remove the hush panel under the steering column. Disconnect C281
(two-cavity connector at base of steering column with two black wires in
the female end and one yellow and one brown wire in the male end). Your
newly purchased resistor goes into the male side of this connector, so
you’ll need to crimp a couple of female pins to the resistor legs. If
you insist on purchasing the VATS bypass from one of the Corvette
catalogs, again measure the resistance of your key pellet and compare it
to the code chart to find your code. It is also possible to reprogram the
PROM to ignore the VATS signal, but that is beyond the scope of this
article.
The real fix came from GM in July of 1988 as TECHNICAL
SERVICE BULLETIN number 88-292. This TSB includes the part number for a
new ignition cylinder that has better contacts. Keys have also been
updated that are slightly longer and have the better contacts. This
virtually eliminates VATS problems caused by connections. You still want
to keep your key clean and dry, but with the TSB competed, you should
enjoy VATS problem free starting for a good long time.