I had been having lots of trouble with the VATS on my '89 IROC. It was working intermittently and the key resistor bypass did not fix that. So I took my dads oscilliscope and scoped the VATS pin at the ECM. I then made a small oscilator circuit to produce a similar signal.

It is a square-wave signal with a period of approx 36 ms at about 5 volts. I used a 558 timer chip (you could use a 555, or 556 too) and powed it off of the 5 volt signal going to the TPS sensor. I cut the wire from the VATS and wired my timer in (pin B6 i think, its blue). I wired a resistor (1K or 10K, i don't remember) from the VATS to ground so it won't light the security light constantly. When I went to start it, it WORKED!!! I was sooo happy. Now I know my car will start every time I turn the key.

Don't forget to bypass the starter enable relay too. I do not know if the signal is the same for all years of VATS modules. But I did play around with the frequency of the signal, and the ECM is not very picky, so don't worry about being real precise. Of course if you are already burning PROMS then bypass it there, but for me this was much cheaper and eisier then buying a new VATS module.

~Joel

 

Smart man! Glad it worked out for you as good as it did!

 

Excellent work. I thought I was the only one who new that trick. I used an HP function generator to diagnose my VATS. I got a pile of NE555 timers. All we need is a miniature etched board and we have an aftermarket product. I replaced mine, not the greatest area where my office is located. Kudos to you