2003 Chevy Impala

You have several computer systems in your car. Which one are you looking for?

Most ommonly it is the PCM that is what controls all of the engine running and the transmissions runnings.

It can go bad due to ages. Shorts. Improper testing procedures

Also, you need not suspect a failing computer unless you have frequent engine/transmission problems that aren't caused by bad sensors. Such as:

If you have a misfire or hesitations/stalls, but your ignition system and related sensors all check out fine. If you have your fuel system checked and that's also in proper working order.

In cases such as this, then your computer should be checked out. But like blackop555 said, unless someone has performed an improper testing procedure, or there's no accident that physically damages your computer, then that's one of the last components that'll go bad on a vehicle.