I have a 2000 S4 that I'm getting ready to sell but just recently encountered an issue with the keyless entry. The remotes (I tried both) no longer function but the locking/security system still works fine. I can use the key to lock/unlock all of the doors as usual and the system still arms/disarms. However neither of the remotes will do anything (I tried replacing the batteries). Any ideas on where to start looking for the issue? I'd like to fix this before I sell the car!!