central locking key fob

I have trouble sometimes opening my car with the key fob. but I don't have trouble locking it. So that give the impression that the signal can reach.

I've tried disconecting the battery and reattaching, then turning the key in the ignition on and off quickly 3 or 4 times. This did work the first, but not the second time.

If anyone tries this don't leave the battery disconected for to long as you might have to put in a code to restart your radio. Any ideas?