A used one is a bad idea if your vehicle does not have the factory anti-theft system. If it does, you can use any computer. If the one you get isn't programmed for anti-theft, it will learn that from the Body Computer the first time you turn on the ignition switch, then work normally. If your vehicle doesn't have it but the used computer you get does, it will teach that programming to the Body Computer. At that point the engine won't start because both computers will be waiting for a disarm signal that is never coming. At that point you will need to replace both computers at the same time with ones without anti-theft programming.