As i am driving, the theft mode light comes on and the car shuts down and won't start again. it has been towed 2x's and they can't find the problem. this is a cadillac dealer working on it.then it will start,get it home and there it sits because it won't start again.any solutions will help. thank you!
Honestly if it's a VATS problem all you need to do is use a meter to test the resistance in the ignition key (on the shaft of the key there is a small black plastic square with a thin metal wedge) Put the volt meter on oms and place the leads on either side of this little wedge in the key, once you have this reading you will need to get a resistor(s) within +/- 10%. Under the dash find the main group of ignition wires, there will be one or 2 much thinner wires cased in a black or orange tube usually they are 2 white wires but unfortunately they can very...from this point it's kind of trial and error and you must be careful because of how thin the wires are. but cut one strip the ends put the resistor in-line if the car starts you made the right choice...sauder and tape, you will want to be gentle with the resistor because they can break pretty easily if you have a couple zip ties splint them around it.....OK if you decide to do this it is making the VATS system void...and if you don't want to try this yourself bring it to a car stereo shop where they install remote starts...they should know all about it!!!
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Re: car just shuts down
If the theft light is comming on it will make it so it will not start i would take it to your local locksmith who has V.A.T.S. (vehicle anti theft system) equipment they can then read your key and make sure there is no problem if the key reads fine have them check at the bottom of the column they can hook up there machine and make sure it is reading the key to the bottom of the switch. Usually this is where the problem is there are only two small wire that go from the ignition cylinder to the harness below the column and after time they will break. Do this and it should resolve your problem. Thank You
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It is possible that the brake light connection was damaged during towing... however it isn't likely.
Understanding where the problem happens is critical. You say it happens when the car is "shut down", but is the key out of the ignition? or is the engine just off? it it actually your brake lights? or just the tail lights? some more info would help narrow it down.
Has anyone changed the part of the ignition switch that reads the key value and sends it to the anti-theft module, it this part malfunctions it will lock you out, and you will be unable to start the car, they are a known fault for all GM lines with factory anti-theft systems, it is part of the ignition switch, but I believe that it alone can be replaced, call your local dealer and ask about the sensor for the VATS key in the ignition, they should know what the part is formally called.
I am going to take a wild guess and say that the security light was on steady before you decided to change the battery. I am also going to guess that it had been on for a while and you never looked into why it was on because the vehicle was starting an driving just fine.
What likely happened is there was a problem with the ant-theft system. The problem was likely minor and the system went into a limp mode of sorts allowing you to continue to drive and start the vehicle with no issues.
the problem with these limp modes is if the battery is disconnected the system shuts the vehicle down as no longer remembers that the previous problem happened when the vehicle was being operated normally. The system now thinks the vehicle is being stolen and is shutting down the vehicle.
You best bet is to tow it to a reputable shop that has experience with these systems to have the problem diagnosed, repaired and relearn the anti theft system.
SOUND LIKE THE THEFT SECURITY PROBLEMS. MOST OF THE TIME.THE IGNITION KEYS OR IGNITION SWITCH KEY LOCK CYLINDER WORN WHERE THE BCM AND PCM DONT RECOGNIZE KEY OR SWITCH SIGNAL.SO THE BCM AND PCM WILL GO IN THEFT SECURITY MODE.THE DEALERSHIP WILL HAVE TO FIX.BECAUSE IF THE KEYS , IGNITION SWITCH AND LOCK CYLINDER AND BCM HAS TO REPLACED.THEY WILL HAVE TO BE REPROGRAM USING DIAGNOSTIC EQUIPMENT. NOT A HOME FIX.YOU WILL NEED TO GET FIX SOON AS POSSIBLE.BECAUSE FAULTY SECURITY THEFT CODE WILL SHUT DOWN VECHICLE FUEL SYSTEM WHILE DRIVING OR IT WILL GET TO A POINT WHERE CAR WONT START NO MORE.THIS FIX WILL COST ABOUT $600.00.
The procedure for reprograming a key,
1 insert key and turn on but do not start, then turn off.
2 wait 15 minutes, turn key on, but do not start, then turn off
3 wait another 15 minutes and you should be able to start engine and drive away. You also have the option to have the car towed to the dealership and let them reset it with their scanner.
Take your chipped key in your driver side door lock. Turn in left and then right then left again. This should get it out of valet mode unless there is a button on the bottom of the dash. Your vehicle seems to be in valet mode which is why it is shutting down on you.
This is a easy fix. Lucky just follow the procedure and your car will start. This is a theft system shut down.
The procedure is. Disconnect battery for a minimum of 30 seconds. ( one post is OK. )
Reconnect battery and get in the car and start as usual 1 time only. When it starts and stops letthe key just return to run position as if it was running. Do not shut it off and if you do you must stert the procedure all over again. i usually put on the emergency brake before i start and that shuts of the driving lights etc.
Just leave the key in on running position and go have a coffee. it takes 15 to 20 minutes for the car to recycle the system. When you come back to the car the flashing theft light will either be off or solid.
Try to start again. If it doesn't go shut it off and turn back on and start as usual. It will start and run and stay running.
The reason you have this problem is something electronic was disconnected whe the battery was hooked up. always disconnect the battery before you touch anything electronic and you will not have this problem.