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VATS decoder module issues...

7K views 21 replies 9 participants last post by  Lonewolf3030 
#1 ·
Where can I find a new VATS decoder module? None of the usual catalogs seem to have it. I'm guessing this is a dealer only part?

I think mine has gone to seed. I've had a couple of VATS issues in the past where the car wouldnt crank. After taking the key out and letting it sit for a few minutes, the system reset and the car started with no problems. Last night, when I got home I parked the car in front of the garage. about 40 min. later it started to rain, so I went out to move it into the garage. Put the key in and nothing. Let it sit for a few minutes and tried again... nothing. Let it sit for about 5 minutes, fired right up. I moved it in the garage and shut it down. This morning when I went to leave, the car wouldnt start. It cranks just fine, but will not fire at all. Fuel pressure at the rail is good, ignition module, cap, and rotor are new, battery is good. The FSM seems to indicate a faulty VATS decoder module (code 46), but I havent tried to pull a code yet. I'm thinking that last night's episode did something to it, and when I shut it down, something in the module went haywire. Sound right?
 
#2 ·
Where can I find a new VATS decoder module? None of the usual catalogs seem to have it. I'm guessing this is a dealer only part?
You don't state what year you have so more than likely it is a discontinued item.2nd hand from wrecking yard and then you would need new key to match the decoder.

Test proceedure
http://www.thirdgen.org/vats_passkey_system

Alternative is to bypass

http://www.corvetteforum.net/c4/rayquayle/vats/vats.htm

http://www.joestradingpost.com/vats/
 
#7 ·
Okay, got a new VATS module sitting here looking at me. My question is, how do I GET to the old one? I know it's behind the dash, I think on the passenger side, but the FSM doesnt show or tell the procedure of what to disassemble to get to it!
 
#8 ·
Found the module location and changed them out. DID NOT solve the problem. Engine still cranks but will not fire. I have good fuel pressure at the rail, I've changed out the distributor module, cap, and rotor, and have a brand new ignition key, but still nothing. The day I got the new key cut, I came home, put it in the ignition, and the car started right up. I killed it and tried it again, and it was back to the crank/ no start situation. I do know I am going to have replace the battery tomorrow evening when I get home, as I'm having to keep it on the charger while trying to start the car. The engine cranks over fine when the battery is charged, but could the battery be causing the problem I'm having? I know I read somewhere that the injectors have to have X amount of voltage in order to operate. I have GOT to get this fixed by Sat. or I'm going to be afoot!
 
#10 ·
There is a min battery volts needed to run car. I would be doing any testing with a fully charged battery to eliminate a low V problem.
Crank and no start indicates that you are not getting the signal to pulse the injectors.
Do you have any current codes?
 
#11 ·
Brand new Optima red top battery installed just now, still no start. I jumpered the A and B terminals of the ALDL terminal, but there are no codes, all I get are the three "12" codes, which repeat, and nothing else. I am noticing that the "security" light on the information panel flashes while I am cranking the engine. This is really starting to get aggravating.
 
#13 · (Edited)
Have you checked if it has spark when it is cranking? Sounds like you could have a bad ECM or even ignition module.

Also, another thing you can do, if it does have spark, is get your hands on a simple test light. Take the test light and put the probe into one of the injector connectors. Then crank the engine, and see if the test light blinks while the engine is cranking.

If the light does not blink, then you can take the probe and connect it to the main harness and check again. If that fails to blink, then you have a wiring problem up to the injectors, or even bad ecm.
 
#14 ·
Swapped out the ignition module already, so it's new. Gonna put a test light on the injectors this morning. I was told that as long as the SES light comes on when the key is turned on, the ECM is working, but I dont know if that's true or not.
 
#17 ·
This gets stranger by the minute. I replaced the VATS decoder module, and still I have a crank, no start situation. I have reached the limit of my abilities as far as diagnostic and test procedures go, so I had the Vette moved to our local Chevy dealership (yeah, I know, but the owner is a Corvette fanatic, as is the service manager, so I feel safe using them). They have tested every wire, every circuit, and etc., and can find NOTHING wrong with the car. They have a VATS simulator which can be plugged in to simulate the VATS module for testing, but in a recent move to their new building, the test leads were lost, so they cant use it. The tech that's doing the work feels that the NEW decoder module I bought is bad. He said it's getting the right voltage coming in, but is not putting anything out to enable the fuel injectors. What are the odds of a brand new VATS module being bad? I have another one that will be here tomorrow, so I'm keeping my fingers crossed. If that's not the problem, I dont know what else to do.
 
#18 ·
-98 Engine Start Sequence

When you start an L-98 engine Corvette, a series of events take place that causes the engine to run. Knowing the sequence will help you troubleshoot no start conditions.

Fuel Rail Pressurization:

When you first turn the key to the “on” position, the fuel pump will run for 2 seconds pressurizing the fuel rails. There is a Shraeder valve on the passenger side fuel rail near the rear of the engine and if you measure the pressure there after the pump runs, you should see between 40-42 pounds of pressure. The reading will go to 38-40 pounds nominal once the engine is running.

Initial Crank Action:

If you then rotate the key to the start position (assuming the anti-theft system has not disabled the starter), the engine will rotate.

Once the oil pressure has reached 4 PSI, the oil pressure switch will close allowing the fuel pump to run. (Note that you should have a black oil pressure switch/sender. It is mounted behind the distributor on the driver’s side and if it is not black, it is suspect due to a run of bad units that stayed in the GM parts pipeline for some time).

The distributor will send a string of pulses to the ECM (Engine Control Module) in response to the engine being rotated by the starter. These pulses continue as long as the engine turns (both starting and running) and if they are not present, the engine will not run.

ECM Reaction:

If the ECM sees oil pressure greater than 4 PSI and the reference pulses from the distributor, it will energize the injector drivers which will begin pulsing the injectors on for 4 ms (milliseconds) periods. (In the L98, all injectors on one side of the engine fire at the same time followed by all injectors on the other side firing at the same time. On the LT-1, the injectors are fired individually at the appropriate time).

The ECM will also pull in the fuel pump relay in effect paralleling it electrically with the oil pressure switch. (If the fuel pump relay fails, you can still normally get the car to start and run unless you can’t make at least 4 PSI oil pressure. This is a “limp home mode” feature put in place to allow for a fuel pump relay failure).

The ECM also monitors the TPS (Throttle Position Sensor mounted on the throttle body assembly) and wants to see .54 volts at this time. If it sees appreciably more than 0.54 volts, it will assume the engine is flooded and the driver has pressed the accelerator to the floor to clear the flooded condition and restrict the fuel flow as a result. (.54 volts during start and at idle from the TPS is very important to both starting and run performance.)

Assuming the ignition module is good (meaning there is a spark of sufficient intensity to ignite the fuel), the engine will “catch”.

Engine "Catches":
 
#19 ·
Are you still having VATS problems? My mechanic says that the wireing may have faded or corroded to the point that the ohms are different from they key code ohms and replacing the wires does the trick. What did you find as I am having the same issue's where sometimes it needs to reset and getting more problematic. My mechanic is right now correcting this for me.
 
#21 ·
I may have a solution for you. As I stated in an earlier post to you I have been experiencing similar problems with the start of the car. My mechanic explained to me how inside the steering column, when you turn the key to start the car it twists the wires inside which seperates the wire inside the shielding, thus creating a "gap" in the internal wireing. That means you are not with a good connection or volts or ohms (I am not an electrician).

First to the location of the VATS in the dash, mine is directly behind the radio and heating/AC unit. Looks just like the ignition with a key in it laying right on top of the carpet.

What I have been doing that works everytime is when I start my car I put the key in, wait a moment, turn it one turn (no dash lights or bells ringing at this point) and wait a moment, then turn the key the next turn (now dash lights and bells light up) wait a moment and if your seat belt is not on, wait for the final bell or "ding" (mine does 5 or 6 "dings"), then start the car. I have done this for a month now without any problems or the car not wanting to start.

As Jerry, my mechanic says, the best solution is to get a "Vehicle Anti-Theft Bypass Switch" (Corvette Central Part # 594361 for 86-89 models) and install this. Now you can turn on-off the VATS any time you want to. For the cost of the Bypass Switch ($59.95) which is relatively inexpensive compared to other solutions and aggravation. And do not forget to go to your Chevy dealer to get your VATS code if you do not know it. Just hand them your key and in moments they will tell you what it is. I just happened to know mine from running all the option codes and the VIN myself.

The best solution however in the long run is to replace all the VATS wireing from steering column on. Since more than likely it is in the column itself.
 
#22 ·
Hey, it's me again. Hopefully I have been of some help for you. Here is what I have also found in my Corvette Central catalog, page 167, right below the Vehicle Anti-Theft Bypass Switch, Modules. You haven't stated your year C4 but listed is 1984 thru 1989. The 1989 "System" is $309.00. Also listed are the 84-86 door switch and 87-89 door switches for VATS. Including the relays for same years. Costs on these are nominal and affordable even on my meager budget as nothing over $40.
 
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