To pair the remote with the receiver:

Pull the c/b
wait 5 sec.
put the c/b back
within 5 sec. press the OFF button on the remote for 1 sec. minimum

The c/b is located in the trunk on the right-hand side in my 2004 3.0D
It shows as "Fernbedienung" which means remote and is c/b #86 5Amps