I've recently picked up an NZ new 1996 (12/95 build) E36 328i.
The car came with 2 keys, both are OEM 3 button ones like below. But one has an LED and takes a single big battery, while the other has no LED and takes 2 small batteries.
They both work fine when used manually, but none of the button functionality works on either.
I've replaced the batteries, but that has made no difference.
Central locking in general seems to work fine, with all doors locking and unlocking together.
My first thought is that they've lost their pairing with the car. I've attempted several different methods to re-pair them, but the car never seems to respond on the final step after pressing the lock button 3 times (although the led lights up on the key).
I've checked all of the Central locking fuses, and they all look fine.
I'm starting to think there is an issue with the receiver in the rear view mirror.
Any help would be greatly appreciated.