Door locks!

[-Dan-]

Hi, right  few weeks back my key fob died so I thought it's ok I'll just use the key in the lock, but I got to say what a job that was, the key would not work took ages for me to unlock it! Now the key I have works in the ign fine and the lock moves both ways, but I can work out why it wouldn't unlock, now I have a feeling it maybe the auctuator or the micro switches in the door lock mech, now if I buy a secondhand unit will it need coding to the car?