I've seen a lot of questions here about disabling VAT (vehicle anti-theft) system. I've seen written posts for fixing this problem with resistors but this is other way how this can be done.
There are two things that are enabled with right key code (resistance); starter enable relay and fuel enable input.

1. Starter enable relay
Relay is located under left side of the instrument dash (drivers view). You'll need to remove trim panel under the dash to be able to see relay. When you remove it, you'll see 2 or 3 relays located on the left side. Starter enable relay is one that is connected with two thick yellow wires, one thick yellow/black wire and thin black/yellow wire. You'll need to cut thin black/yellow wire and connect one end of the wire that is going to relay terminal to ground. The other end of wire (it's going to CCM) needs to be isolated. This will enable cranking even if your key isn't right code or your CCM is gone bad.

2. Fuel enable input
ECM is connected with 4 22-pin connectors that are all different colors. Signal that enables fuel delivery goes to pin 6 of the red connector. It is blue wire. This wire needs to be cut and one end that is going to pin 6 of red connector needs to be connected to ground. The other end (it goes to CCM) needs to be isolated. This will enable fuel delivery even if your key isn't right code or your CCM is gone bad.


All of the above procedures should be done with disconnected battery.
Also, this fix is valid only for year model '90 and '91 that are equipped with '727 and '730 ECM's or corresponding GM remanufactured units.
I have tested this on my friends '91 and it works without problems.

I hope this will help someone.

 

thanks for that. Will put that one in the car incase it happens when i'm on the road.

see ya on the road

 

I wish it would work for a 92!
Bernie

 

tip #1 works for starter enable.

tip #2 does NOT work for fuel enable on any -727 0r earlier -165 ecm/ vette chip that i have tested...you need a 30 Hz sink of the ecm 5v output...see GIjoes' vats write-up for a free schematic to build a vats (signal) sim

 

http://www.vatssucks.com/

 

It would seem to me that the easiest way to disable VATS is to reprogram the chip to take away VATS.

Haven't tried it but that's the way I'm leaning to get rid of the dreaded VATS.

 

AFAIK, on the 92, that doesn't quite work... Nathan Plemmons tried it, and the way the ECM works, it should, but won't. Most odd.

You see, with the 90-96, the CCM sends a VATS ok code to the ECM/PCM. On later (94+) PCMs, it's doable, but on the earlier ones, it's not... Ask Tom Piper, TJ Wong or Nathan... I am sure they can give you the right info.

Generally speaking, on the later cars, the VATS is quite reliable, it's on the earlier cars, with all the relays and crap, that have problems. The resistor is the best bet for the later cars.

 

As I said, I tested this on '91 that has '727 ECM. Engine starts and
runs normally.
Maybe it allready had, disabled VATS in EPROM?
We grounded both starter and fuel enable at same time.

 

That's good to know. Just an FYI on the earlier 165 ECU Simply cutting the fuel enable circuit and grounding it will not bypass the circuit. The ECU looks for a square wave signal from the VATS control module. This is a pulse rather than a constant ground.

 

I turned it off on my chip for my '93 and it still works.. something weird about the 92-93 ECM CCM combo.. damit!

 

Well that changes my plans.

Although I haven't had a problem with VATS since I disconnected to after market Viper system that the previous owner had installed. I kinda of wanted to keep the Viper for the key fob door opener but I think that's what was messing with VATS in the first place.

Thanks for the info.