Anti-Theft Systems for GM Vehicles
GM has used a variety of anti-theft systems on their vehicles. When you get a no start, intermittent start, or start then die, you should diagnose the anti-theft system before you start replacing starting components. A tell-tale sign that you’ve got an anti-theft problem is a flashing “Theft” light. Here’s a brief primer on each system and what to look for.
Each GM anti-theft system disables different components. Some disable the engine starter, while others enable the starter but disable fuel injectors. None of them disable spark. So, first understand the difference between vehicle theft deterrent systems.
VAT
The VAT, or vehicle anti-theft was used primarily on 1986-88 Corvettes. The key had a pellet that was married to the vehicle anti-theft module at the factory. If the lock cylinder was turned or bypassed with the proper key installed, the system would disable the starter and kill the injectors. You could NOT perform a system “relearn.”
PassKey I, and II
Similar to the VATS system, these vehicles also used a pellet key. You can identify this system by looking at the key. It has a black resistor pellet with a thin metal edge running along the key. The system enables the starter, but shuts down the injectors after initial startup. So the vehicle would start, then die. This system has a “relearn” feature. It was used on these vehicles
Buick
Century 97-01
Park Avenue 91-96
LeSabre 92-99
Riviera/Reatta 90-01
Regal 94-99
Roadmaster 94-96
Cadillac
Eldorado 89-01
Seville 89-97
Fleetwood 92-96
Deville 90-99
Allante 89-93
Chevrolet
Camero 89-01
Corvette 89-01
Caprice/Impala 94-96
Lumina/Monte Carlo 95-97
Oldsmobile
Cutlass Supreme 94-97
Aurora 95-00
Regency/88 91-99
Toronado 90-93
Pontiac
Firebird 89-01
Grand Prix 94-96
Bonneville 92-99
PassKey III
This system uses a special key (PK3 stamped on the shoulder of the key) with a transponder under the rubber cover. The receiver module is located next to the lock cylinder. When the key is positioned next to the lock cylinder receiver module, it energizes the transponder which sends a coded signal to the receiver. The receiver module checks its memory to see if the signal is correct. If it is, the module sends a signal to the PCM to enable the engine. If the value is valid, the indicator light will remain steady for 2 seconds. You cannot test this system with an ohmmeter. You need a scan tool. If the signal is not correct, the PCM disables the injector and the starter and flashes the light once per second. If an illegitimate key is used or a system problem exists, the light flashes twice per second.
The system is used on:
Buick
Lesabre 2000-on
Park Avenue 97-on
Cadillac
Seville 98-on
Deville 2000-on
Oldsmobile
Aurora 01-on
Pontiac
Bonneville 2000-on
GM Minivans
Venture, Montana, Silhouette
Passlock
This system allows starter operation, then kills the injectors 1-2 seconds after startup. This is a “Hall-Effect” system. The key cylinder housing has a small magnet that rotates past the Passlock sensor. The sensor is powered and detects the rotation. The voltage on the sensor then drops to a specified value (there are 10 different values). There’s no pellet in the key. So basically this system is checking to see that a thief has not popped the lock cylinder to steal the vehicle. you have to perform a Powertrain Control Module (PCM) relearn procedure (need a programming scan tool). The Passlock system was used on:
Buick
Skylark 96-98
Chevrolet
Cavalier 95-on
Impala 2000-on
Malibu 97-on
Monte Carlo 2000-on
Oldsmobile
Achieva 96-on
Cutlass 97-on
Intrigue 98-on
All GM trucks 98-0n
SYSTEM DIAGNOSTICS
PassKey I and II System Diagnostics
There are 15 different key codes. Measure the resistance of the key pellet by connecting an ohmmeter to each side of the key pellet. Once you find the resistance value, remove the lower dash panels and locate two small wires (both white) that run down the base of the steering column. Disconnect the electrical connector where those wires terminate. Then connect an ohmmeter to that electrical connector and insert the key. The reading you get at the end of the two white wires should match the resistance value you got from the key. Next, turn the key. The value on your meter should NOT change or drop out. If it does, you will have to replace the key cylinder. It is COMMON for the wires to break from the key cylinder.
If you have the PassKey system and the engine cranks, runs, and quits AND the THEFT light is on (for about 5 seconds), here are the tests you should perform:
1) Disconnect the electrical connector at the deterrent module. Then turn the ignition switch to RUN while you test the voltage between the dark blue wire in the theft deterrent electrical connector (the one you just disconnected) and a ground point. You should see 5 volts. If you don’t get that voltage, check for an open or short between the dark blue wire and the PCM that supplies the voltage to the module.
If you DO get the 5 volts, turn the ignition off and reconnect the electrical connector. Pierce the insulation on the same wire (with a pin) or back-probe the wire in the connector. Turn the ignition to RUN. The voltage should now read 2.5 volts. If not, replace the theft module. THAT assumes you have already conducted the key pellet test (explained above) and that it passes the test. If you see 2.5 volts and the vehicle still won’t stay running, check the fuel pump relay.
Here’s how it works, The lock cylinder reads the resistance of the pellet in the key and transmits that data to the theft module. Meanwhile, the PCM provides 5 volts on the dark blue wire. When the theft module determines that the proper key has been inserted, it partially grounds the voltage on the dark blue wire. The PCM initially provides fuel injector pulse, but if it doesn’t sees a voltage drop on that dark blue wire, it cuts off the fuel injectors. That’s why you get a crank, start, engine shut down.
So, if the vehicle starts and then dies, AND THE THEFT LIGHT FLASHES, the module is not getting the proper signal from the lock cylinder or the module is bad.
Passlock
Testing this system is similar to the Passkey I and II systems. You want to check the voltage at the bottom of the steering column as you insert the key and rotate it check the yellow signal wire (should be 5 volts before you start the testing). Turn the key.
The value should drop. If it does not, you will have to replace the key cylinder. The “control module” for this system is built into the instrument panel control (IPC) in early years. In later years, the system is controlled by the Body Control Module (BCM), the Electronically Controlled Orifice-steering Assist (EVO), IPC and other systems. If you have to replace the lock cylinder or any of the control modules,
Passkey III
You cannot check this system with an ohmmeter. You will need a scan tool to watch the operation of the system and find the trouble code. Once you get the trouble code, follow the diagnostic procedure based on the specific code.
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© 2007 Rick Muscoplat
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Rick, I re thought the situation, and think you are correct. Just fix the Passkey System. I am getting power to the injectors, but the computer isn’t switching to ground. By your email, I am assuming that I have either a bad computer, bad passkey box (located behind the breadloaf), bad ignition or bad Theft Deterrent Module. I replaced the ignation, so I assume it is one of the other three. I will have a mechanic check the system per your instructions and go from there.
Rocky
I HAVE A SURCURITY LITE TURNED ON AND I HAVR TRIED NUMEROUS TIMES TO TURN ON MY OLDSMOBILE BRAVADA 2002 AND NO LUCK. I HAVE RUN OUT OF EVERY SOLUTION AND IM WONDERING IF MAYBE YOU HAVE ANY NEW INFORMATION THAT YOU CAN INFORM ME OF. I HAVE TRIED A TEN MINUTE SEQUENCE AND START IT FOR ABOUT 40 MINUTES AND NO LUCK THERE. I HAVE ALSO TRIED DISCONNECTING THE BATTERY AND WAITED 2 HOURS TO TRY TO START AND NO LUCK THERE EITHER. I HAVE ALSO LEARNED THAT IT COULD BE DONE WITH A LOCK SMITH AS FAR AS THEM STARING IT FOR ME. BASICALLY WHAT IM ASKING IS IF YOU HAVE ANY OTHER OPTIONS FOR ME TO START MY VEHICLE I WOULD REALLY APPRECIATE IT BY EMAIL. THANKS SO MUCH FOR YOUR TIME.
You didn’t tell me what vehicle you own or what parts you’ve replaced. If you haven’t fixed the root problem, there’s no way you’re going to get this to start by doing the relearn procedure.
I have 95 monte carlo assumed bad cylinder wiring or pass key however I cannot find the 2 white wires as described. Are they connected to the electrical ignition switch harness? I count 8 on ign switch and another 10 on either side of that connector for power windows steroe etc I assume but I do not see the 2 thin white wires anywhere. Any pictures currently I have access to elec switch on column and in process of removing air bag steering wheel to access cylinder for replace.
I have a 2000 Oldsmobile Silhouette I just purchased. When changing the spark plugs, wires, oil, and starter,…. the car would not start back up. I had a friend who works for GM run a test on it, and the theft deterrent code came up. He told me to replace the pass-lock module on the ignition and I did with one that I got from a junkyard off a 1999 Silhouette. Then did the relearn test and it still wont start. I’m not sure of what to do now and was hoping you have some ideas.
I’d put in a new passlock cylinder. These things have such a high failure rate (almost 100%) that I’d never trust one from a junk yard. You can buy a brand new one for $66 here
I have a 2003 Chevrolet Malibu. I drove to my son’s house (about 3 miles) and visited for about 2 hours. I went out to go home and tried to start my car. The anti-theft light started flashing when I turned the key on, the car would not start. How can I disable that anti-theft device and get my car to run without it? I don’t care if the anti-theft device won’t work but I need the car to run. The car has a little over 89,000 miles on it. My son is a mechanic and he put a computer on it and everything else is working fine. Any advice would be appreciated. I am 71 years old and I don’t need to get out and break down somewhere. Thank you
2005 Pont Montana SV6 – drained the battery, jumped it, and now Service Theft System error message is displayed. Can’t use factory remote start either, but remote door lock/unlock/open still works.
Ideas?
Thanks!
Obviously the jump start knocked out some electronics. Happens very often these days. Best way to jump start is NOT with jumper cables but with a jumper pack.
I have 2002 Buick Rendezvous. Starts on a cold start every time, but if I run to the store and come out 15-20 minutes later, car starts then immediately dies and just cranks over. If I keep cranking and the battery is almost dead it will start. Does this sound like a Passlock problem?
If the security light isn’t flashing then it’s not a passlock problem. If you’re not getting any flashing security light, I’d suspect a bad coolant temp sensor or a clogged fuel injector. A bum coolant temp sensor would give the computer the wrong engine temp. Since you said it starts good cold, at least we know that it’s reporting a cold engine. But if it’s still reporting cold once the engine is hot, then the computer would be injecting too much gas, making for long crank times. A dirty MAF sensor could also cause the same problem. The MAF tells the computer the temp of the incoming air so it can calculate air/fuel mixtures.
On the other hand, a leaking fuel injector would bleed all the fuel pressure out of the fuel line while you’re in the store and flood the cylinder. Then it would take a few seconds to build pressure and clear the flooded condition. The clue to that is really rough running right after a “hot-soak” startup and lots of black smoke coming out of the exhaust once it does start. Also, check this by putting your foot all the way to the floor and holding it there while you crank. The “clear flood” mode tells the computer to shut off fuel to the injectors and opens the throttle to let in lots of fresh air. If the car starts faster that way, you’ve got a leaking injector.
Of the possibilities, I’d start by cleaning the MAF sensor. Find out how to do that here. Next, I’d replace the coolant temp sensor. They’re less than $20 and it takes less time to replace them than it does to test them. At the same time, I’d pour in a bottle of Chevron Techron or CRC Guaranteed to Pass fuel system cleaner. Those are the two best fuel system cleaners.
Thanks for the info Rick. One more question, the security light does flash, but only after I let it crank and crank until the battery is almost dead and then the car starts. So, looks more like a passlock problem possibly? I will check the other items mentioned as well.
I have 2002 Buick Rendezvous. Starts on a cold start every time, but if I run to the store and come out 15-20 minutes later, car starts then immediately dies and just cranks over. If I keep cranking and the battery is almost dead it will start. Does this sound like a Passlock problem?
Rick says:
February 15, 2012 at 6:33 pm
If the security light isn’t flashing then it’s not a passlock problem
I have a 1997 chevy lumina, it has the passkey system. I performed the test and got the 5 volts with key inserted. When i turn to the on position I get a higher reading of about 12 volts. I replaced the theft module and got an even higher reading of about 14 volts and the same result of crank but no start. I am sure that this is the root of the problem as my fuel pump relay and injectors are shut down. The last thing i am thinking of trying is to switch out the ecm unless these details can bring me an answer to my problem. Any help will be greatly appreciated.
I have a 97 buick skylark,……2.4 engine
It has been having a strange buzz under the dash on drivers side.
Have power locks but not windows, that buzz sounds when you hit the lock button
I have been having trouble with Anti-thief for a while, but if I would hit the lock unlock button it would start, some times the radio wouldn’t work after and would have to hit unlock lock and it would come on.
Well it wouldn’t start and I was trying to start it it would start and die in a few seconds or if I put it in gear. Then it started having a delay with the key and starter, then the starter wouldn’t crank at all. Thats where I am now nothing no crank at all by passed straight to starter and it cranks fine, tried to start and died. Have the dash apart thinking it has to be that passlock system. Does all the disable theories work or do I need to do something else. I would like to disable it completely and never have an issue again. I have read all the ways to disable just want to be sure that is the way to go. I don’t want this to happen again I drive 400 miles to the doctors so I need it fixed. Thanks so much and I hope you can help me I will check back tomorrow before we start this again.
I have a 2005 Chevy Equinox. The key would not turn in the ignition, replaced the housing and the cylinder. Keys turns with no problem except now it won’t start and the anti-theft is blinking. Battery won’t stay charged either. Lights and radio work too.