bad computer?

I have a 2003 pontiac Montana van I had an o2 sensor change and I had a security light flashing for a whole year when I bought the van. When they reset the van the did want to come on but the security light came on. What could it be? Is it a bad compiter? When I turn the key the lights raisin and everything comes on?

Why was the O2 sensor changed?

So the car started before the O2 sensor change, but after repacement, it will not start?

Not exactly sure what they did...did they try to clear a code with a scan tool or did they disconnect the battery for any reason?

On the security system for this vehicle, if you have a problem with it, but it happens AFTER THE CAR IS STARTED, then the Security light will come on.....the vehicle will continue to start, but the Security light will continue to come on because it is in a default mode.....

Now, if after replacing the O2 sensor, the battery was disconnected or codes were cleared, if you go to start the car, and the problem is present while cranking the vehicle, then the car wil not start, because you are no longer in the default mode.....

Vehicle should be scanned for "B" codes, which most code readers/scan tools can't read....quick way to check this....if fuel pressure is ok, spray carb cleaner into the intake while cranking....if it starts and runs as long as you spray, then the injectors are not firing because of the security problem....

Look at your owner's manual, to see if the Security system you have is PassLock or PassKey?

It started after they change the o2 sensor they said that they did not disconnect any battery cables they use a scan tool? They use that tool that connects at the bottom of the steering wheel I don't have a handbook can I find one online ?



Why was the O2 sensor changed?

So the car started before the O2 sensor change, but after repacement, it will not start?

Not exactly sure what they did...did they try to clear a code with a scan tool or did they disconnect the battery for any reason?

On the security system for this vehicle, if you have a problem with it, but it happens AFTER THE CAR IS STARTED, then the Security light will come on.....the vehicle will continue to start, but the Security light will continue to come on because it is in a default mode.....

Now, if after replacing the O2 sensor, the battery was disconnected or codes were cleared, if you go to start the car, and the problem is present while cranking the vehicle, then the car wil not start, because you are no longer in the default mode.....

Vehicle should be scanned for "B" codes, which most code readers/scan tools can't read....quick way to check this....if fuel pressure is ok, spray carb cleaner into the intake while cranking....if it starts and runs as long as you spray, then the injectors are not firing because of the security problem....

Look at your owner's manual, to see if the Security system you have is PassLock or PassKey?

it had a check engine light I had to get it changed


It started after they change the o2 sensor they said that they did not disconnect any battery cables they use a scan tool? They use that tool that connects at the bottom of the steering wheel I don't have a handbook can I find one online ?

Let's start over.......

After they replaced the O2 sensor, did the car start and run? If it didn't, they couldn't get it to start?

If it did, how long was it before it wouldn't start?

Did you check your owner's manual to see if your vehicle has Passkey Or PassLock, for a security system?

The car started and run when they got it down from the left to park it and bring me the keys to pay for services. After going back to my car trying to get it start it would not start when I went out to start after paying for the o2 sensor getting fixed. I dont have the owers manual i looked online and its a pass key III

Let's start over.......

After they replaced the O2 sensor, did the car start and run? If it didn't, they couldn't get it to start?

If it did, how long was it before it wouldn't start?

Did you check your owner's manual to see if your vehicle has Passkey Or PassLock, for a security system?

Hate to ask this but, did you actually see the car start and run like they said, or is that what they told you?

If it is PassKey III, then the shaft should have PK3 stamped on it or a symbol, like a circle with a cross inside,stamped on it....

Turn your key to "on", don't crank the vehicle...look at the SECURITY or THEFT light on the dash, does it go out after 3-5 seconds? If it stays on, than you have a PassKey problem....

What kind of garage is this? A GM dealership? A chain? Or local garage?

Like I previously said, if your vehicle, developed a PassKey problem, AFTER THE CAR WAS STARTED, your vehicle will go into a default or backup mode....your vehicle will continue to start...this looks like what happened BEFORE you bought your car....now, if you clear codes or should disconnect your battery, this "resets" this mode...if the problem is still there, now when you try to start the car, because the problem is there BEFORE STARTING THE CAR, a code will be set, and the car will not start.....

I have seen cars that have had remote starts put in....they tie into the "exciter circuit" that surrounds your lock cylinder...if this was previously done than that would have to be replaced.....

So what happened to the vehicle? Did the Garage look at it? Did they say it would cost you more? The LEAST THEY COULD HAVE DONE, was to check for codes in the vehicle for you......PassKey problems create "B", or body codes.....code readers and cheap scan tools can't read them.....don't know if this garage has a scan tool that can do this....

But we have to start somewhere.....so insert the key, and just turn to on, and if the SECURITY/THEFT light stays on, that's where you have to start......If it is staying on, than the starter enable relay will be disabled and the vehicle will not even crank over....

I did see them move my car with someone driving it, I did as you have told me and the security light still comes on. Could it be that the key was magnitized cassing it to lose programming?

OK, if you turn the key to "on"(do not try to crank vehicle), the SECURITY light should come on for three to 5 seconds, and then go out.......if it stays on, you have a PassKey problem.....do you have another key that you can try?

With Passkey III, there is a transponder build into the head of a key.....when inserted into the lock cylinder it becomes "excited", and transmits a radio signal....this signal is then picked up and sent to the theft deterrant module, which enables the starter and also sends a fuel enable signal to the PCM(computer).....

Since your SECURITY light has been on since you bought the vehicle, this should have been taken care of from the beginning....if you had bought this from a dealer, you should have brought it back to be fixed, at his cost....

As I said before, you need a garage with a scan tool capable of reading "B" codes......in this case, a GM dealership may be your best bet....

I found someone who said that they could get on the road for $ 497, I think they where talking about what you have stated about fixing it by putting in b mode. It's garge that services gm modules. Is that a good price or should just tell them that I need the van put back into b mode

OK, if you turn the key to "on"(do not try to crank vehicle), the SECURITY light should come on for three to 5 seconds, and then go out.......if it stays on, you have a PassKey problem.....do you have another key that you can try?

With Passkey III, there is a transponder build into the head of a key.....when inserted into the lock cylinder it becomes "excited", and transmits a radio signal....this signal is then picked up and sent to the theft deterrant module, which enables the starter and also sends a fuel enable signal to the PCM(computer).....

Since your SECURITY light has been on since you bought the vehicle, this should have been taken care of from the beginning....if you had bought this from a dealer, you should have brought it back to be fixed, at his cost....

As I said before, you need a garage with a scan tool capable of reading "B" codes......in this case, a GM dealership may be your best bet....

Think about it.....

How can anyone give you a price without diagnosing it first?

Any parts involved?

Well I had towed my car to another shop to see if they could fix it. A mechanic and it had a dead battery cell but their was and someone left a tool near the battery. Also he thought it was a relay switch and they re program the key. The car started up they parked it and when I got their I put the key and it's not working again what could it be ?

Re read posts #7 and #9......

I can't help if you don't answer questions.....

It's a local garage. They claim to have use the scan tool. They changed raly switch and it still is not working

Sorry, if you don't answer questions I ask, how can I possibly help you?

I found out that the security module went bad in the car. How does that happen?

The theft deterrent control module can go bad...it's electronic......more often than not, I see them go bad when someone tries to install a remote starter/alarm in the vehicle...they compromise the wiring to the module and then the module has to be replaced...