By Terry Jones

 

In 1986 GM introduced the VATS or Vehicle Anti-Theft System.  The system is set to read one of 15 resistor values which must match the value of the pellet on the ignition key.  If the system detects an incorrect or non-existent resistor value it disables the engine starter and produces a no-crank system for four minutes.  After this time the system resets and you can try to restart the engine.  Some newer systems are called PASS Key II.  This lock-out was happening to my 1990 intermittently but with increasing frequency. 

 

After reading about the system and discussing it with Cam Chabot, a technician at Myers on Merivale Rd, we decided to bypass the system rather than try the more expensive route of replacing the ignition cylinder and keys.  He was of the opinion that because the fault was so intermittent that it was probably the result of 20 year old worn wires which move every time the ignition is turned. 

 

The tech disconnected the security system under the dash and soldered the appropriate value resistor on the vehicle side of the VATS connector.  The system is satisfied that it is always seeing the correct resistance to match that on the key pellet so it should never lock out the starter.  This process was described in a website article passed on to me by Ron Rail.  The article was intended for those wishing to bypass the system and install a remote starter but it works just as well for this problem - if in fact the fault was diagnosed correctly.


From Answers.com - here is the response to the question - How Can You ByPass the VATS device?

 

Vats Bypass

O.K. before you go cutting wires I want you to go get your handbook that came with the car, it's probably in the glove box, look up anti-theft and do what the book says. I did this and instead of cutting an orange wire all I had to do was turn off the radio and hold down the 1 and 4 button. 

VATS - Vehicle Anti-Theft System GM introduced the VATS or Vehicle Anti-Theft System in 1986.
Basically the VATS security system must read one of 15 resistor values to allow the vehicle to start. Use an incorrect value, you'll lock out or put the vehicle into a no crank situation for up to 10 minutes. (although I really never sat and timed it) Therefore, your well advised to have an ohm meter. (if your as lucky as me, it seems to always be the last resistor in the pack that works) Use a meter, or it makes for a real long day !

I read somewhere, that when GM introduced the VATS system it significantly reduced the theft of GM vehicle equipped with such a system.

The VATS system disables the engine starter if the systems module detects an incorrect, or non existent resistor value at the time of ignition. Within the Key there is a small built in resistor pellet.
The system was enhanced to also include a fuel shut-off, sometime later. 

As I mentioned before, there are 15 different resistor values. As long as you are within 5% +/- of the measured value, you'll be able to bypass the system.
The newer system is called PassKey II. (Passlock 2)
VATS and the PassKeyII systems basically operate the same, except they moved the resistor into the lock cylinder.

 

BYPASS for a Remote Starter
Most everyone who is visiting this site is looking for a bypass for use with a remote starter.
If you are in a lock out situation and you need to know how to bypass the VATS, PassKey I or PassKeyII systems, this is also your quick fix. 

To bypass GM VATS system:
Drop the steering column cover to access the VATS wire harness coupler. Ordinarily, the wire will be 2 white wires or possibly white and purple. GM has used a variety, but they should be within in a colored jacket, equally as varied in color, and are 2 light gauge wires. There will be a connector.
With the Key inserted, Un-plug the connector, and measure the KEY side of the harness
Record the value.
Refer to the Chart. Look up your value on the chart. It should be one of the values on this chart, or very close. (Must be within 5% +/- )
Use Color
Orange, White, Red, Black RES390 - 392 Green, Red, Orange Black RES510 CN 523 Blue, Gray Brown, Black RES680 FW 681 Gray, Gray, Violet, Black RES910 GP 887 Brown, Brown, Orange, Brown RES1.1K KA 1130 Brown, Yellow, Violet, Brown RES1.5K N5 1470 Brown, Gray, Violet, Brown RES1.8K UN 1870 Red, Orange, Violet, Brown RES2.4K XB 2370 Orange, Black, Brown, Brown RES3.0K GA 3010 Orange, Violet, Yellow, Brown RES3.6K NP 3740 Yellow, Violet, Green, Brown RES4.7K FY 4750 Blue, Black, Yellow, Brown RES6.2K C5 6040 Violet, Green, Black, Brown RES7.5K XY 7500 White, Green, Orange, Brown RES10K KB 9530 Brown, Brown, Gray, Red RES12K UW 11800 

Alternatively, measure the resistance of the VATS Resistor Pellet by placing the resistance of the VATS Resistor Pellet by placing an Ohm meter set at 20k ohms on each side of the Pellet.
Average the 2 values, and select the value closest this average. 

To disable the system, insert this resistor, into the CIRCUIT side of the connector.
Set volt meter at 20k setting touch both sides of key pellet take reading and compare to chart below
Acceptable ranges)
1 402 ohms (acceptable range 386-438)
2 523 ohms (acceptable range 502-564)
3 681 ohms (acceptable range 650-728)
4 887 ohms (acceptable range 850-942)
5 1130 ohms (acceptable range 1085-1195)
6 1470 ohms (acceptable range 1411-1549)
7 1870 ohms (acceptable range 1795-1965)
8 2370 ohms (acceptable range 2275-2485)
9 3010 ohms (acceptable range 2890-3150)
10 3740 ohms (acceptable range 3590-3910)
11 4750 ohms (acceptable range 4560-4960)
12 6040 ohms (acceptable range 5798-6302)
13 7500 ohms (acceptable range 7200-7820)
14 9530 ohms (acceptable range 9149-9931)
15 11800 ohms (acceptable range 11328-12292)
Quick Note: if you have the type of key that has the resistor pellet on the key you can check the resistance simply by measuring the resistance with a multimeter by connecting a lead to each side of the black pellet where the metal point is in the middle of the pellet. 

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