VATS writeup almost completed. Tech gurus inside!
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
Originally Posted by redrose
most folks control elec circuits by NOT putting power into a device until it is active...GM often does NOT design their circuits this way, they put power into a device and complete the ground connection to activate...there are reasons, too much ''theory'' for here, just always remember it is done that way on many circuits on your vette.
the ecm ''generates'' the signal and sends signal to the vats module... the vats module ''grounds'' that signal to let the ecm know that vats is happy with the ign key resistor value... a simple ground switch would have been too ez to bypass, in the minds (?) of the designers, so the ground MUST oscillate at abt 30 Hz for the ecm to be happy (fooled the thieves for at least 30 seconds with the 30 hz thing)...it is ''nice'' to know if the ecm is ''happy'' with its oscillating ground--a test connection point on the signal wire to the ecm and a convenient ground point will allow you to see the ''apparent'' voltage that the ecm signal is at--if correct this will be 2.5-3.0 vdc and if 5.0vdc (nominal) or ''0'' vdc, the ecm will not fire the injectors
the ecm ''generates'' the signal and sends signal to the vats module... the vats module ''grounds'' that signal to let the ecm know that vats is happy with the ign key resistor value... a simple ground switch would have been too ez to bypass, in the minds (?) of the designers, so the ground MUST oscillate at abt 30 Hz for the ecm to be happy (fooled the thieves for at least 30 seconds with the 30 hz thing)...it is ''nice'' to know if the ecm is ''happy'' with its oscillating ground--a test connection point on the signal wire to the ecm and a convenient ground point will allow you to see the ''apparent'' voltage that the ecm signal is at--if correct this will be 2.5-3.0 vdc and if 5.0vdc (nominal) or ''0'' vdc, the ecm will not fire the injectors
Melting Slicks
Joined: Jul 2006
Posts: 3,356
Likes: 1
From: Chesapeake Va
Originally Posted by redrose
most folks control elec circuits by NOT putting power into a device until it is active...GM often does NOT design their circuits this way, they put power into a device and complete the ground connection to activate...there are reasons, too much ''theory'' for here, just always remember it is done that way on many circuits on your vette.
the ecm ''generates'' the signal and sends signal to the vats module... the vats module ''grounds'' that signal to let the ecm know that vats is happy with the ign key resistor value... a simple ground switch would have been too ez to bypass, in the minds (?) of the designers, so the ground MUST oscillate at abt 30 Hz for the ecm to be happy (fooled the thieves for at least 30 seconds with the 30 hz thing)...it is ''nice'' to know if the ecm is ''happy'' with its oscillating ground--a test connection point on the signal wire to the ecm and a convenient ground point will allow you to see the ''apparent'' voltage that the ecm signal is at--if correct this will be 2.5-3.0 vdc and if 5.0vdc (nominal) or ''0'' vdc, the ecm will not fire the injectors
the ecm ''generates'' the signal and sends signal to the vats module... the vats module ''grounds'' that signal to let the ecm know that vats is happy with the ign key resistor value... a simple ground switch would have been too ez to bypass, in the minds (?) of the designers, so the ground MUST oscillate at abt 30 Hz for the ecm to be happy (fooled the thieves for at least 30 seconds with the 30 hz thing)...it is ''nice'' to know if the ecm is ''happy'' with its oscillating ground--a test connection point on the signal wire to the ecm and a convenient ground point will allow you to see the ''apparent'' voltage that the ecm signal is at--if correct this will be 2.5-3.0 vdc and if 5.0vdc (nominal) or ''0'' vdc, the ecm will not fire the injectors
Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 15
From: backwoods upstate ny
Originally Posted by edcmat-l1
Thats not exactly correct. First, if the module pulled the 5v ref to ground, it would never see a voltage diff across the resistor in the key. There are 15 different resistances, and all of them are so close together, if it just pulled the ref voltage to ground it would never be able to differentiate between the pellets. It (the ref voltage) is pulled down, but thru a series of resistors that are very accurate, and compare the RETURN voltage to what has been calibrated in the controller. It then sends an oscillating signal to the ECM to let it know its happy with the pellet value. In general its a good system, has worked well on lots of cars for a long, long time. I have been diagnosing and repairing them for years. Have owned a VATS interagator for 10 years or more. Hope this helps
Thread Starter
Team Owner
Joined: Jun 2001
Posts: 26,196
Likes: 0
From: Orlando FL
St. Jude Donor '08-'09
ahh thanks guys, the ecm signal makes a LOT more sense now. I think I understand how it all works enough to finish the write up on that segment.
as of 10-27-06, added the following:
Schematics for 1990-1993 Corvettes Ignition, Starting, Passkey and Universal Theft Deterrent Systems.
94-96 coming later this weekend or as soon as I have time.
www.joestradingpost.com/vats
as of 10-27-06, added the following:
Schematics for 1990-1993 Corvettes Ignition, Starting, Passkey and Universal Theft Deterrent Systems.
94-96 coming later this weekend or as soon as I have time.
www.joestradingpost.com/vats
Melting Slicks
Joined: Jul 2006
Posts: 3,356
Likes: 1
From: Chesapeake Va
Originally Posted by redrose
appreciate your attempt to help, but unfortunately you are wrong...there are 15 possible ignition key resistor pellets for the vats module INPUT and they are totally divorced from the vats OUTPUT...which is not really an output, but rather a ''sink'' or ''ground'' of a signal voltage from the ecm...the vats module does not ''send'' a signal per se, it is merely the ''catcher'' for the signal from the ecm ''pitcher'', and any catcher that the ecm sees will cause the ecm to ''enable'' the injector fuel delivery...build one (vats sim) and see, it works
Melting Slicks
Joined: Apr 2002
Posts: 2,118
Likes: 0
From: St. Charles, MO Route 66 Corvette Club
GIJoe: this is excellent work for those who want to bypass the VATS system. Please be advised this should be posted in the C4 tech section. Also be advised the tech section will not accept new information such as this 
Melting Slicks
Joined: Jul 2006
Posts: 3,356
Likes: 1
From: Chesapeake Va
Originally Posted by redrose
appreciate your attempt to help, but unfortunately you are wrong...there are 15 possible ignition key resistor pellets for the vats module INPUT and they are totally divorced from the vats OUTPUT...which is not really an output, but rather a ''sink'' or ''ground'' of a signal voltage from the ecm...the vats module does not ''send'' a signal per se, it is merely the ''catcher'' for the signal from the ecm ''pitcher'', and any catcher that the ecm sees will cause the ecm to ''enable'' the injector fuel delivery...build one (vats sim) and see, it works
PS I have no doubt about the operation of a vats sim, I just dont have any exp with them, as I'm not in the habit of bypassing the system. not that I have anything against doing so. To each his own.
Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 15
From: backwoods upstate ny
Originally Posted by edcmat-l1
Upon further review, the correct operation of both cicuits in question lies somewhere in the middle of both our theories. The key pellet circuit is grounded on one side, not thru a circuit switch but directly to ground. The vats decoder applies 5 volts to the other side, via an IC and parallel resistor, to check against for calibration. The decoder to ECM signal is sent from decoder TO ECM along a 5 v ref circuit sent FROM the ECM. The 5v ref is provided by the ECM, the decoder toggles it to ground to inform ECM. So you are correct that ECM is "pitcher' of the 5v ref. Yet the SIGNAL is actually provided by the decoder, it does the switching.
PS I have no doubt about the operation of a vats sim, I just dont have any exp with them, as I'm not in the habit of bypassing the system. not that I have anything against doing so. To each his own.
PS I have no doubt about the operation of a vats sim, I just dont have any exp with them, as I'm not in the habit of bypassing the system. not that I have anything against doing so. To each his own.
prolly doesn't appeal to you if you are getting paid to repair em tho
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Melting Slicks
Joined: Jul 2006
Posts: 3,356
Likes: 1
From: Chesapeake Va
Originally Posted by redrose
no theories on my watch...simple correction for an assinine idea ...it WORKS...toss ALL the vats hardware in the trash bin--no wet key , worn key, or sick vats module problems ever again...for under $10...
prolly doesn't appeal to you if you are getting paid to repair em tho
prolly doesn't appeal to you if you are getting paid to repair em tho
Thread Starter
Team Owner
Joined: Jun 2001
Posts: 26,196
Likes: 0
From: Orlando FL
St. Jude Donor '08-'09
Originally Posted by scranage
Joe - Thanks for the writeup. I am going to tackle the replacement of my lock cylinder soon, I'll take some pics if you want to add them.
YES please if you can! that will save me the trouble of taking mine apart when it doesn't need to LOL.
If you could also write down all the steps needed... like if you have to remove any dash panels, or any extra tips that might help someone else like "Tool XYZ made the job a LOT easier" etc...
also, if you could note how long it takes too.
anything would be of great help for someone else that needs to have this done in the future
I plan to get all those that helped contribute to this up on there for a thank you note as well...
Team Owner
Joined: Oct 2000
Posts: 96,443
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From: Fort Knox, KY
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Whenever I lock the doors on my car either with the key or the PDL switch, the VATS sets the horn alarm off about one minute after the door is closed.
I've checked the power door lock switches and courtesy light functions and they seem to be ok. There are no DIC trouble codes.
Is there a module or any sort of underhood or under-dash electronic component that could have failed and caused the VATS to sound the horn like this?
I've checked the power door lock switches and courtesy light functions and they seem to be ok. There are no DIC trouble codes.
Is there a module or any sort of underhood or under-dash electronic component that could have failed and caused the VATS to sound the horn like this?
Burning Brakes
Joined: Nov 2005
Posts: 908
Likes: 1
From: Colorado Springs Colorado
Originally Posted by GIJoe
YES please if you can! that will save me the trouble of taking mine apart when it doesn't need to LOL.
If you could also write down all the steps needed... like if you have to remove any dash panels, or any extra tips that might help someone else like "Tool XYZ made the job a LOT easier" etc...
also, if you could note how long it takes too.
anything would be of great help for someone else that needs to have this done in the future
I plan to get all those that helped contribute to this up on there for a thank you note as well...
If you could also write down all the steps needed... like if you have to remove any dash panels, or any extra tips that might help someone else like "Tool XYZ made the job a LOT easier" etc...
also, if you could note how long it takes too.
anything would be of great help for someone else that needs to have this done in the future
I plan to get all those that helped contribute to this up on there for a thank you note as well...
Racer
Joined: Jun 2000
Posts: 292
Likes: 3
From: Chico CA
Originally Posted by BadjerJim
Beautiful work, Joe.
I know that I'm going to have to face this on my 1990. Just a matter of time.
I know that I'm going to have to face this on my 1990. Just a matter of time.
Tried the spare key, but realized that I'd tried the starter over 3 times, and didn't have time to wait. Sheesh.
Suddenly VETTELESS until I get this figured out. Sheesh.
Joe: I'll contribute what I learn about the 1990 model!
