WW7

I spoke to a family friend who happens to be a GM tech guy a few days ago.. He told me something I didn't know about vats, and I have not seen it ever mentioned on here....

There are 2 versions of vats, Passkey 1, and Passkey 2.. Pass key 1 is in the C4 Corvettes until 88, Pass key 2 is in the C4s from 89 until the LT1 was introduced into the line at which time the ecm controlled the vats... Passkey 1 will set a 4 minite timer to lock out any attempts to start the car, if you try to start the car before the 4 minites is up, you reset the 4 minite timer again, blocking your attempts .."Now", here's the thing I didn''t know, Passkey 2 also sets a 4 minite timer, but unlike Passkey 1, after the 4 minite timer is set, if the proper key is used, or the key is cleaned and is read by the Vats key reader, the car will start, even before the 4 minites is up...I have read everything I could find on here about vats and have never seen any of this mentioned... How many of you guy knew this???...WW

don hall

Not I ..... thanks

Deakins

I knew that there was such a thing as Passkey 1 and Passkey 2 (I worked a little on passkey 2 in tech school) but hadn't ever delved into the differences. Good info!

MrWillys

I know there is Passkey 1, 2, 3, and now Passlock. My 2004 c5 has a resistor pellet in the key, but I'm not sure which version it is.

http://sethirdgen.org/vats.htm

leesvet

yeah, I knew that in the 80s VATS you HAD to wait it out and ANY attempt before the 4 min time had passed would reset it and you could potentially sit there all damn day if you tried 2 seconds too soon each cycle...

I did not know that GM programmed the next generation of VATS to start anytime the key reader was correct...

What I am a little surprised at is the 4 minutes....

for the longest time I was always told 15.
It was only in the last few yrs that I came across the 4 minutes lock-out.

WVZR-1

Your friend has mislead you!

There's way more required to explain than I have time for but for you to understand the VATS system on your particular C4 you need to see the 9D section of the FSM. There's nowhere that it's explained that a correct resistance can be introduced into the system and be "keyed on" without the required "time out". The "time out" has changed through the years but not by much.

The TDM for '86 - '88 was the same and if replaced it required replacement of keys because it was serviced with a "random" resistance value. The odds of receiving the same value 1 in 14 and it certainly wasn't a frequent repair. This was first just VATS.

In '89 the TDM was changed to the same as used in the F-body, Buick, Oldsmobile and Cadillac for many years. It was serviced with a learn procedure and there was no requirement to replace keys as long as you used a "NEW" module. This is the way I recall it. I've seen this referred to PassKey I because it was capable of being learned but it's simply VATS. FEDS was also introduced.

In '90 the TDM was removed and the circuit moved to the CCM or BCM until end of production. PassKey II is used to describe this frequently.

The double-sided C5 is similar to the later C4's with CCM/BCM.

See 9D in your FSM for the education.

There is also a difference in 30Hz and 50Hz but that can get involved.

WW7

The reason I asked my friend this question about the vats is because I had a bad vats key that the reader would not read...I could use the bad key and the car wouldn't start, turn right around a few seconds later and use the good key and it would start right up...I asked him why my car would do this, because I always heard you had to wait 4 minites for the system to clear...What I wrote above is what he told me was the difference....
WVZR-1,, You know I respect your opinion , you have a great deal of knowledge.... I don't know a whole lot about electronics on the C4s , but this is how it's working on my 89, I have tried it a few times...That's all I know.....WW

WVZR-1

Read the 9D section of your FSM. I don't have an '89 but I would assume this - you've got a problem likely with the TDM module. You just replaced the key cylinder in your car I thought? That would mean you needed all new keys. This happens with your new keys OR this is the way your system responded BEFORE all of the column work?

I'd be interested in what your FSM tells you!

Once a non-recognized key is turned to the "crank" function of the key cylinder there is a "time-out" required. That is the most simple description of the VATS regardless of which it is.

WW7

WVZR-1 , I will read the 9D section of my FSM and let you know what I find, I sure don't want to be giving out bad information on here......
One other question, is the TDM the same as the Vats Reader Module?? I have had Vats eliminated in my tune, shouldn't this stop the TDM from working, or am I off base on this?...
I have eliminated Vats in my tune , Installed the resistor plug under the dash to eliminate vats from reading the key in the cylinder, and I intend to bypass the Starter Enably Relay under the DIC...Will this completely eliminate Vats from my car?? Is there anything else I need to bypass or eliminate???..Vats really does suck.........Thanks WW

WW7

WVZR-1......Here is what it says in my FSM-9D..What does this mean to you?? It says down at the bottom that if the proper resistance isn't read, the timer will not reset a second time, allowing the driver to perform an immediate restart using the proper key.Then it says that theres a 2 to 4 minite time out no matter what key you use... The last few sentences sound like a contradiction to me...The way I read it is, even if the vats key reader sees a bad code the second time you try to start , it won't reset the timer allowing the driver to try a restart immediatly...How do you read this WVZR-1???........Leave it to GM to make things clear as mud......WW

Cliff Harris

The key wording in the FSM picture from the FSM posted by WW7 is "two to four minutes". The circuit is analog and subject to the tolerance of the components. There is no "exact" time and it varies from module to module and therefore car to car.

I wrote an article a few years ago on the innards of the VATS module in my '86:

https://www.corvetteforum.com/c4-tec...schematic.html

I asked the Forum for somebody to volunteer and send a VATS module to me so that I could experiment with the timing but I never got a response.

gungatim

The way I read that FSM excerpt is time out for unauthorized key, ie. completely wrong resister pellet or no pellet. No time out if the resister is correct but slightly out of tolerance. If resistance too high and it goes back to spec with a cleaning or re-insertion it will start. I believe there is a +/- 2% tolerance to the resistor value. When I bypass these, I usually shoot for the low end of the range rather than the middle.

Once you bypass VATS, you never go back!

corvettenorway

http://www.joestradingpost.com/vats/index.html

five7kid

When I got my '96 in January, I only got one set of keys. Against advice I've seen on corvetteforum.com, I bought two ignition key blanks off of eBay (100% feedback seller). When they arrived, both measured within 3 ohms of the key I had (all right at the design value, not at the edges of the tolerance).

I had Ace Hardware cut them for me. When I went back out to try them, the first one started the car right up. I tried the other one, and while it allowed the switch to turn, the engine didn't turn over. I put the original back in, turned it to start, nothing. Got out the owners manual and read the instructions, waited a couple of minutes and tried the original key again, nothing. Waited 4 minutes, it started. Put the 2nd new key back in, tried it again, nothing. Had to wait another 4 minutes for it to start (I was afraid someone was going to call the cops on me, sitting out in the parking lot trying to start a Corvette for all that time...).

Went home, measured the resistance of the keys again, got nothing for the key that didn't work. Pressed harder on the probes, it read the proper value again - I suspect the Ace employee ran the wire wheel over the resister while deburring after cutting the key, dislodging the wire - that key has been set aside.

Anyway, my experience does not line up with the contention that the later VATS system will allow the car to start up right after putting in a key with the proper resistance. Or what the owners manual says (haven't checked my FSM).