What problem do you have when your security light comes on in your 2002 Chevy impala?

The Impala, as well as other GM models, have a passive theft deterrent called 'Passlock' which will prevent your car from starting if there was an attempted theft or other unauthorized entry into the ignition. However, this same system is prone to randomly and sometimes frequently engage itself even when the car is being used properly.

Solutions: 1) If the car will not start or "crank", turn you key in the ignition to the 'on' position and leave it there for a minimum 20 minutes. After 20 minutes, turn the key to the 'off' position for two minutes. Now attempt to start the car. This is a built-in feature of the Passlock system to override the security lock. 2) If this does not work, you may need to have the car taken to a dealer (a regular mechanic will not be able to guarantee a fix). They will check for a diagnostic code, and if one is present which relates to this system, they will advise that you replace the BCM (Body Control Module), ignition cylinder, and the ignition switch. This will be around $800 depending upon your dealer and where you are located. Unfortunately, unless you systematically isolate each component, you may not know which part is actually causing the problem. However, the most likely culprit is a faulty ignition cylinder or a bad BCM. The BCM's are known to be "buggy".

GM is well aware of this problem, but they will not issue a recall.

Hope this helps a little.