Hello All I have a 1999 Mercedes A170 I have a strange problem with the alarm and central locking system. It was all working fine and then out of the blue a couple of weeks ago, I tried to lock the car and arm the factory fitted alarm with the remote and it would not lock. So I tried turning the key in the driver's door and that would not lock the doors either. I then had to go inside and lock all doors manually and use the key to lock the boot and driver's door. Now - I can confirm that the central locking system is working to a certain extend, because when you use the internal button under the hazard light switch, the doors lock. Also if they are locked using the switch when driving, the minute you open the driver's door after ending a journey, the doors unlock. Also - I noted that the alarm wont auto arm like it normally does if you leave it unlocked. I have tried: Disconnecting the car battery negative terminal and re-connecting after 10 seconds. I have tried re-registering the key as per the instruction manual: press lock button twice and then turn key to position 2 within 30 seconds. Neither have worked on either of my keys. Does anyone have any suggestions? Is there a way to re-set the alarm and/or central locking system, perhaps? Thanks in advance!