My 1996 300D traditional key is not unlocking/locking the doors. I changed both batteries in the key and the mirror was replaced a few years ago.

The green or red lights on the mirror stopped flashing. I am unable to lock/unlock the car directly with the key at the drivers side door. I place key in the key hole and turn key but door locks did not move.

Is there a chip in the key that requires a match with door lock for security purposes? Do I need a new key? Where can I start to diagnose?

Thanks for the guidance as I am not able to lock car at all.

So do you only have one key fob? I have three. One starts the car most of the time and always locks/inlocks the doors. This key fob sometimes needs to be inserted more than once or turned over to finally start the car. The second key fob only starts the car and does not lock/unlock the doors. The third key fob only unlocks/locks the doors and does not start the car. You may be headed in that direction.

Len

Thanks for the response.

I have only 1 key which is the switch blade key that folds into the black casing. The car does crank and start. I can't lock doors either thru the remote or manually thru door key hole.

Ah, sorry, looks like the key fobs changed between your 1996 and my 1999. Mine doesn't have the folding blade. Hopefully someone with more info than me will provide some help.

Len

The key for a '96 E300D is not chipped, I know that much. There are no sensors in the door handle and ignition switches like there are in later cars. That you're not getting the red/green flashing lights indicates, well, something. What puzzles me is why the physical key will not operate the door lock.

When I had my '96 I stopped using the remote fob key after a security system issue prevented me from starting the car one afternoon. I cleared the problem by using the physical key to cycle the locking system. After that I stopped using the remote fob and started using a simple physical key only. I had a new one cut by the dealer. Never had an issue after that.

Start by checking the central locking system fuse and vacuum pump in the trunk, those often fail on these models. Since the key doesn’t work in the door either, it could be a mechanical issue with the door lock cylinder or linkage.

UPDATE for 96 300 D (W210) with regular switch blade flip key and remote

I disconnected the battery for 5 hours to reset PSE. I tested again with key and by pressing lock/unlock button in car and none of the doors, trunk or fuel lid lock or unlock. I hear the pump humming (low sound) for a few seconds when commands of lock or unlock occur but no movement of locks. Alarm is activated/inactivated with the key remote.

My PSE part # is 210 800 0648. I pulled years ago one at a yard that part # is 210 800 1148. Would this work on my car? If I have to replace PSE, does the replacement have to be coded? I have just a simple switch blade key that has a single round push button at center of key. What should I try next to get vacuum system working again? Thanks.