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94 Buick LeSabre No Security Light,Vats Kills engine after start


Ratt643
11-28-2007, 06:24 AM
I hope that someone has had better luck than me with this VATS. I recieved this car from a guy who wanted to drive it daily, Seem his Father in law was not able to drive any longer. The car had not been started in a year. I cleaned eveything up(inside and outside the car and gave it a tune up. My freind started driving it and it would occationaly start then die.After 20 minute or so,it would eventuly stay running.Found that the wires on the ecm connector (red) were cut to disable CEL.After resoldering the wires back to their correct configurtion, the CEL comes on but I don't get a security light.The tumbler assy is bad so I cut wiring at the column and inserted the correct resistor for the vats(according to a web site that listed the resistance for all the GM keys. Is the VAts unit itself bad and Where is it. I check the bulb in the instrument cluster an foud it to be good. I heard it was buried in the dash deep.I've tried another ecm and no luck. Any help would be appreciated. Thanks

steven david
11-28-2007, 09:51 PM
the anti-theft module is right above the glove box and the box is easy to remove. had a vats problem coding on my sons 1994 lesabre last spring. check out the thread in tips and maintenance for lesabre, it's titled"diagnostic tips for vats" by steven david . around the same time i was working my problem , another member reported a shorted injector as the cause to his same problem

HotZ28
11-28-2007, 10:10 PM
My freind started driving it and it would occationaly start then die.After 20 minute or so,it would eventuly run. Can you expand on the part above? The security (VATS) system, will not cause an engine that is running to die! :shakehead

Ratt643
11-29-2007, 10:01 AM
the anti-theft module is right above the glove box and the box is easy to remove. had a vats problem coding on my sons 1994 lesabre last spring. check out the thread in tips and maintenance for lesabre, it's titled"diagnostic tips for vats" by steven david . around the same time i was working my problem , another member reported a shorted injector as the cause to his same problem

Thanks, I'll check that out as soon as I get state side!

Ratt643
11-29-2007, 10:06 AM
Can you expand on the part above? The security (VATS) system, will not cause an engine that is running to die! :shakehead

According to a good friend of mine who is a technician at our local Chevrolet dealership, The vats will shut down the injectors if it doesn't see the right resistance from the key after engine start. After so many attemps the vats is supposed to disable the starter relay,but mine has been by-passed. I'll check for a shorted injector when I get back stateside. Thanks for your service.

HotZ28
11-29-2007, 10:19 PM
According to a good friend of mine who is a technician at our local Chevrolet dealership, The vats will shut down the injectors if it doesn't see the right resistance from the key after engine start. After so many attemps the vats is supposed to disable the starter relay,but mine has been by-passed. I'll check for a shorted injector when I get back stateside. Thanks for your service.

Your friend is partially correct, but that is not how the TDM works! :shakehead
If the resistance is correct, either from the bypass resistor or key, the TDM will send a Pulse-Width Modulated signal to the PCM, and then the PCM will enable the fuel injectors. The TDM also operates the Start Enable Relay (SER) that allows power to reach the starter solenoid when the key is turned to the START position. If the TDM does not recognize the key or bypass resistor, it decides a theft attempt is in progress and it will go into anti-theft mode. In this mode, the TDM will:
1) Turn on the “Security” warning light on the instrument panel. (This may or may not happen with a bypass resistor installed)
2) Prevent starter operation by not turning on the Start Enable Relay.
3) Send a signal to the PCM telling it to disable the fuel injectors.
4) Disable the key recognition circuit for three minutes.

As you can see, the TDM controls two functions when you attempt to start. First, it sends a pulse width modulated (PWM) signal to the PCM to allow injector pulse and then it allows the start enable relay to energize. These two functions happen almost simultaneously. It would be very unusual for the TDM module itself to fail – except perhaps if it has been subjected to a “voltage spike” or other problem that has occurred within the vehicle’s wiring. If that were the case, the TDM would not energize the Start Enable Relay. :grinno:

Ratt643
11-30-2007, 05:11 AM
Is the TDM seperate from the VATS? If it is, where is it located? I never have had the security light come on even before I installed the resistor. I wouldn't put it past this car that it had the battery cable pulled while running(voltage spike). I checked the security bulb in the instrument cluster and it is ok. What next?

spinne1
12-01-2007, 04:25 AM
Ignore the VATS system. Your problem is not that. You have the same symptoms that almost every stall post from that era car has. The common faults to cause it are: crank sensor, ignition module, MAF sensor, and possibly fuel pump/pressure. Those are the main ones. Other things can be involved as well. As HotZ says, VATS will never stall your car once running.

Since you have the check engine light, check your engine codes (paperclip on spots A & B on the under-steering-column-on-black-plastic-under-dash-shield ALDL wiring harness connector--turn key to run (but NOT start) and watch the light flashes beyond the "1" "2" which indicates the system is working and note the codes).

HotZ28
12-01-2007, 08:24 AM
Is the TDM seperate from the VATS? If it is, where is it located? Since the mid-’80s, General Motors (GM) has used three different theft deterrent systems, but they are all passive, meaning its activation is automatic. It’s operated by communication between a control unit and the ignition key through the ignition switch. If the switch is vandalized, operated with the wrong key, or the Class 2 communication link is disrupted, the engine won’t start.

The Vehicle Anti Theft System (VATS) was first installed on the 1985 Corvette. The Personal Anti-Theft Security System (PASSkey) replaced VATS in 1988, and while there are some differences, VATS and Passkey I and II all work the same way. There is no radio communication involved; the system merely looks for the ignition key’s unique electronic signature. The older Passkey systems all have a pellet imbedded in the ignition key that communicates with the Theft Deterrent Module (TDM). Passkey II does not use a seperate TDM (module) so the same security functions are built into the Body Control Module (BCM).

Passkey III and the newer Passlock systems were introduced in 1998, but the earlier systems weren’t completely phased out until 2003. Passkey III uses radio communications between two modules. There is a small chip in the ignition key called a transponder. When the key is inserted into the ignition switch it sends a code to the vehicles computer through a receiver coil mounted to the barrel. Once the computer has identified it as a valid key, it enables the starter and fuel management systems.

Are you absolutely sure that the loss of injector pulse is the reason for the engine stall? Have you used noid lights for testing injector pulse?

Ratt643
12-01-2007, 03:56 PM
I have tried to download codes but my scantool will not link. I tried my friends AutoXRay and it will not link. I ordered a remanufactered PCM and installed it, still will not link. I have not tried the injector pulse but will. I have replaced ignition module, MAF ,checked fuel pressure and regulator.Charging system is charging 14 volts. Have not tried crankshaft position sensor.Still wonder if one of the injectors is shorted out. It sux being half way around the world and just now get some more idea's. Oh well, be going home on Friday and will start to check car. Keep those thoughts and ideas coming!

HotZ28
12-01-2007, 09:20 PM
You need a scanner that will link to a 94-95 OBD1.5 ECU. Generic scanners will not connect. You can use an Actron CP9145 or CP9150. Check with your local shops to see if anyone has a scanner capable of reading the 94-95 OBD1.5 ECU.

steven david
12-02-2007, 08:11 PM
to hotZ28; your right , it was not the vats system that caused a start then stall immediatly condition. it turned out to be the ECM , even though the code was for "security breach". I did explain that. but numerous posts at the time were pointing to the vats system as the answer

Ratt643
12-03-2007, 03:25 AM
Do you think the problem could be in the PROM? When I changed the ECM, I had to transfer the old PROM to the new ECM. Like I said, there was no change in the car, so reinstalled the old ECM.

steven david
12-08-2007, 09:43 AM
I used the old prom with a pcm from auto zone 90$. did you ever check the voltage from the anti- theft module? the 1994 lesabre seems to be a transition year for the obd and vats,creating a lot of confusion,so i'm trying to only relay past experience and not guess at answers. good luck!!!

Ratt643
12-12-2007, 10:21 PM
Well, After finally returning home,I looked behind the dash above the glove box and saw a green connector just hanging there.I then went to a salvage yard and looked at another LeSabre and found a small box connected to it. I bought the box and got the resistance value from the key. A trip to Radio Shack netted me the proper value resister for that Theft Deterent Module.
I returned home, connected the TDM and the resister. Turned the key on, the securuity light came on and when started, it stayed running!:lol: I don't know how whoever worked on this thing before managed to make the car stay running without the TDM! Thanks to all of you for help on this part, now I have to start a new post for another problem. Thanks again!

reli247@sbcglobal.
05-30-2008, 11:01 AM
how did you fix the problem for the security system

BNaylor
05-30-2008, 12:35 PM
how did you fix the problem for the security system

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