Got a MK4 golf and the issue im having is basically the remote central locking doesnt work on the fob. The red LED flashes so the key is working but i cant seem to sync it to the car.

The other key the remote locking works on that but it wont start the car, this key is also bust on the plastic so of no use really other than as a spare.

How do i sync the remote to unlock/lock the car?

Its a 2001 model MK4.

Found loads of guides on the net, none of which have worked.

Thanks