Central locking

Hi everyone, I hope I have the right section this time. I have just bought an 96 A8, I was after something as quick as my old scooby and as comfy as the old lexus so I hope ive got the right car this time around, (no 53) anyway to the point, the main problem I have is the central locking, it all works with the keys but not the fobs (checked batteries) does anyone have an idea what the most likely cause would be? I have checked the fuses and they are ok. What is the central locking pump and where can I find it? could this be the cause?

[B@fink]

its in the boot on the passenger side behind the lining almost directly under where the ariel is. The central locking is air powered and you should hear a faint hum as the pump pressurises to move the locking that lasts for a few seconds (any longer and there may be a leak) If the ariel seal leaks it could get in and upset it so it's worth checking i suppose. If its on a 96 it could have the infrared cl (i don't know the change over date), are you aiming the key at the right part of the car? you can't just be near the car like with radio cl, you have to point it at the b pillar area i beleive.

Does anything work on the fob - does the boot release work?

Hi, thanks for the reply, I cannot hear any hum from the rear but when you lock it with the key you do hear a short quiet beep ( sounds like car horn but a lot quieter) As far as I know everything else is working from the key all the doors open, petrol cap and boot opens,. I will have a look at the pump when the weather gets better. Is there any way of testing it and if I was to replace it, would the keys need to be re-programmed?