Perhaps one of the mods/admins can make this a sticky. I know i've posted it a few times, and it might help to just have it up there.
Some day in your GM vehicle, you might go to start it and the anti-theft system may activate. The anti-theft system will do various things. One, it may delay the running of your car and illuminate the Anti-Theft or Security light. Or, it may keep your car from running at all.
For your Cavalier (95-99 at least) you will have what is called the PASSLOCK system. This system basically will keep you from starting the car without the key.
Parts to the system are the Gauge Cluster, the PCM, and the PASSLOCK cylinder (ignition cylinder). Any time you replace any of these parts, the anti theft system will activate. When you turn your key the passlock cylinder will make a resistance code using a hall-effect sensor. If the resistance code is correct it will sent a password to the PCM. If the PCM doesnt recieve the password in a certain ammount of time, it disables the car.
What happens when my PCM doesn't recieve the password in time?
In this case the PCM will go into what's called short tamper mode. This will disable the car from running for around 4 or 5 seconds. It does so by simply stopping the injection pulse. Basically, the fuel injectors have been switched off. Then you can try again.
If it happens 3 consecutive times the PCM will then go into long tamper mode. This time it will disable the vehicle's fuel injectors for around 10 minutes.
If either mode has been activated, 2 things will happen. One, the Security light will flash. 2: the car will usually start but it will only run for about 1 second, and then die.
So how do I do the re-learn?
Ahh, the fun part. At least you dont have to get dirty.
1) If you were trying to start the car, first you'll need to remove the key.
2) Insert the key
3) Turn the key to the "ON" position. DO NOT TRY TO START THE CAR
*If you're doing this to a higher end model such as a Grand Prix or Grand Am that has automatic headlights,
you may want to set the parking brake before hand so that you dont drain the battery*
4) Leave it sit like that for 11 minutes (10 minutes 59 seconds is not enough)
5) The security light at the end of this period should be off. So go ahead and turn off the key, but dont take it out.
*NOTE: you may have to do this 3 times in a row, but most of the time once is enough*
6) Start the car.
This should complete the relearn procedure. If you continue to have problems, you may need to look into repairing something in the system.
Cars with a BCM (as the 00+ cars do) will have the PASSKEY or PASSKEY 2 system. The parts are different with this system, but the relearn will work the same way.
This will also work on other GM cars, such as the N-body or W-body if you ever know of someone having a problem with it. PASSKEY 3 and 3+ is the system that has the chip in the key. And these steps will not apply to that.