Hey guys, with the last custom chip I burned I decided to turn off the VATS in the chip and just see if it would work. I found a locksmith today that had the proper key, sans resistor, and had them make a copy. For $1.30 what do I have to lose right?

I decided just to be safe that I wouldn't try that key straight out of the locksmith because if it didn't work I wouldn't have the 10 minutes to spare waiting for it to reset and I would be late for work. When I got to work I shut the car down, pulled out my new key and stuck it in. It actually turned, so far so good, at least I know it was cut right. Went to start the car and nothing. I tried my VATS key and sure enough, dead.

I went inside and proceeded about my job. I came back out and with my proper VATS key it fired right up. So my question is, if the VATS Select checkbox does not turn off the VATS, why is it there and is there any way to turn it off? Does it just have to have some sort of resistor key but not necessarily the correct one? If that's the case it defeats the whole purpose in my book.

 

Is there a chance that VATS is somehow fail-safed in the Chassis Control Module?

I cannot understand, unless for some reason the change did not happen. Being in the IT bizz, I can tell you that when you THINK a change has been implemented, it really hasn't.

 

Well I just pulled my chip and download the BIN file. It did keep my changes, so as far as the ECM is concerned it should be off.

 

I'm in.

Based on my understanding of the VATS process, there are two parts to the equation.

Part I is the start enable relay. The VATS reads the key pellet resistance and if satisfied, supplies the ground for the start enable relay, your engine turns over(assuming all the other series parts work). Any thief can get an engine to spin via the starter. We're talking voltage to the control side of the solenoid. And yes, thief must also get the primary and secondary voltage thing working. Suspect jumping a few wires could do this. This brings us to VATS Part II.

VATS Part II. This part involves a second signal provided by the VATS. When attempting start, the ECM runs a 5 Volt signal to the VATS. The ECM wants to see what the VATS will do with the 5 Volt signal. If the VATS drops the voltage to around 2.5 volts, the ECM thinks the VATS has recoginized the correct pellet resistance and the ECM will pulse the injectors, assuming it has an RPM reference signal. This is the hard part for the thief.

From now on I'm guessing. A chip may may be able to suppress the need for a voltage signal drop from the VATS. I doubt it can suppress the start enable relay. If the car didn't turn over, this would suggest the ground for the start enable relay was not available. If you hooked up a scanner and scrolled down to VATS, (assuming new modified chip), the VATS may say Yes or Enabled, forgot exact response.

Hope I got at least 70% of this correct. I like C's.

Anyway, that's my guess. The X's and O generators probably have the correct answer.

dlmeyers 90 coupe zf6 3 speed shocks

 

From what I can tell changing the EPROM did nothing to affect the system at all. For example, if maybe it would have just made it work with ANY resistor key, assuming it used the resistor in the key as part of a circuit or something.

In this case it would have work when I put my original key back in, but rather it was locked out just like it had the wrong key and nothing had ever changed.
I guess I'm still not 100% on how the system works. I would have thought that unchecking that box would make it ignore the system completely and send all the proper signals down the line. In the end it almost has to boil down to a YES / NO "are these conditions met" setup. I would have thought that unchecking that box woudl have forced that to an unconditional YES.

 

Yes VATS is also controlled VIA the CCM

 

Ok fair enough. So what exactly then does the VATS enable in the ECM do, and what if anything can be done to disable it in the CCM?

I was hoping for something that would be pretty easy to turn on and off in case I ever wanted to use it again, no cutting and splicing.

 

You will have to double check the Service manual about the VATS and CCM. Not sure what can be done to be honest.

 

The VATS and the ECM/PCM.

The ECM must receive a go signal from the VATS. When the ECM sees a go signal, ie, voltage drop to around 2.5 volts, the ECM will pulse the injectors assuming the engine is cranking. The VATS, in essence, tells the ECM it is OK to pulse the injectors and allow fuel flow through the injectors at the programmed rate. PULSE/NO PULSE. Computers like those type decisions, so I'm told. Without the signal voltage drop, ECM does not pulse the injectors.

Without a ground for the start enable relay, no engine cranking, no primary and secondary ignition pulses, no RPM reference signal. Car is on static display. If your car did not crank, that would be part of the start enable relay/VATS function. Remember, the VATS module is looking for the pellet resistance. No correct resistance, no start enable, REGARDLESS of how you somehow trick the ECM. The start enable relay signal DOES NOT come from the ECM. It comes from the VATS module after reading key pellet resistance.

Now, as far as your custom chip goes, I have no clue how it interfaces with both the CCM and ECM, just CCM, or just ECM.

As far as something easy, I don't think GM had that in mind when they designed the system. Fact is, I think they wanted to make it very difficult to bypass the system. If it was fast and easy, thieves would have really appreciated that. Remember, when you install a permanent VATS resistor, you are NOT bypassing VATS. You are bypassing the cylinder lock pins that connect with the key pellet. That's it. No more. Your VATS is functioning as designed in that it recognizes the correct resistance, (granted, a fixed resistance hard wired), provides a ground for the start enable relay, and drops the 5 Volt ECM signal to around 2.5 volts. Understand you do not have the fixed resistor installed?

Is your VATS misbehaving? If it is not screwing up, I would leave it alone, but only my opinion. Whatever.

Just for reference, between 86-89, the VATS was a separate module. In 90, they added some code to the CCM and put the VATS function there.

Do you have the factory service manual. I may be able to direct you to a better understanding than my typing allows.

dlmeyers 90 coupe zf6 3 speed shocks


[Modified by dlmeyers, 8:18 AM 10/30/2002]

 

Currently my VATS is not acting up, but it has in the past and left me stranded.

I wasn't trying to trick anything any more than it would be tricking the car to change the rev limiter. It's a function that tunercat displays in the ECM switch table. It's called "VATS Enable" It was checked in the original program. Now seeing something like that I think you would think what I thought. A simple computer YES/NO for using this system or not, how much easier can you get?

Obviously it didn't work, but now I'm just trying to find out why that option is in the ECM? It has to do something, I just don't know what it is yet. It obviously doesn't do what I was hoping it would do.

 

After pondering this for another day, I might have an answer. Does it control the security light on the dash? Reason I ask is this:

When you disable the cags at the transmission you still get the 1 to 4 light on the dash if it meets the requirements. You have to disable it as well in the computer in order for that light not to show. Now I don't believe (not sure) that if you disable the cags in the computer that it will affect the operation of the tranny. Maybe the same applies in the VATS operation?

Just a theory.

 

I thought about that, or maybe it's the factory alarm? I know one way to check, be right back.

 

Security light still functions normally, as does the factory alarm.

 

I know from past experience that disabling VATS from the computer ONLY, and in an original VATS equipped car, won't disable VATS completely, as there is also the hardware part of it still in the car.

BUT, if you were to transplant an LT1 engine in a hotrod, disabling the VATS from the computer will make the engine run. (instead of dying every 5 seconds)

 

Am away from my Snap On parameters manual so this is not definite.

When connected to a stock ECM with the Snap on scanner, one of the fields shown is VATS ENABLE/YES NO, something like that.

Believe this is the feed back loop for the ECM reporting what the ECM is seeing for a VATS response.

When I get home, the Snap on book comes out and will see if this is bidirectional and can be selected. Doubt it. Suspect it merely reports the ECM VATS status, ie, good signal yes, bad signal no. Otherwise, I submit thieves would be buying more scanners however, if your'er burning chips, that would be entirely different and no knowledge of how the code is executed.

dlmeyers 90 coupe zf6 3 speed shocks

Who knows.


[Modified by dlmeyers, 12:01 PM 10/30/2002]

 

Sorry I'm so slow gettin' back to this thread....finally went back over the wiring diagrams that I agonized over when I was having problems with the vats.
The vats module has 2 "sides" to it. As stated above there is the 5v signal sent to the ecm that tells the ecm to pulse the inj. This is the "side" that you can turn on and off in the program-by unchecking, it also will not store a code for vats failure.
However the start enable ground on side of the module is independant from the other "side". So it will still not turn over.
If you have a stick, uncheck vats in the program and then bump start-it will start then. Why GM designed it that way? Go figure....
Also the vats module can fail on only one side-if it malfunctions on only the start enable ground on side it won't set a code! Makes it a lot of fun to figure out then.....

 

Reason for design is antitheft. A thief can get the car to crank. Getting the injectors to pulse through an ECM is more problematic. Further, along with the voltage drop from 5.0V to around 2.5 volts is a proprietary HZ signal riding on the 2.5V. Even more security. This will not be found in most manuals.

Not a bad system actually. These and similar systems are why some crooks have switched to stealing with tow trucks and flat bed trailers. Besides, thieves really aren't that attracted to older vettes. If you gambling 5-12 years in the big house, wouldn't you pick something like a new BMW?

dlmeyers 90 coupe zf6 3 speed shocks

 

Hey Nathan,

I was HOPING this thread would continue on until some resolution was given.

I'm wondering if one had NO VATS system that has to activate/complete the start circuit THEN would disabling this in the PROM cause the ECM to avtivate the injectors during start??

Anyway I'm hoping some more of the rocket scientist here will post back with more good info.

Regards,