This issue is a failure of the internal door lock actuator which is failed in the lock position which is causing the door not to open.
Mercedes a class rear door wont lock.
First you can replace the door lock actuator which can cost from 150 to 450 depending on if you try to fix it yourself or have the dealer fix the problem.
It does not work with either the central locking or auto lock on movement of the vehicle.
Frosty149 sep 20 2017 5.
If a door unlocks but will not lock again then replace the door switch.
On those models the door lock actuators may fail causing the door lock to bounce up and down several times.
You likely have a shorted door lock actuator which you can replace with a new unit for the lock that is not working.
I have mercedes benz c class estate 2009 model that has developed a door locking issue.
Try the battery disconnect again maybe a few times.
The actuator will have to be replaced which will require the door panel to be removed and with the door closed this won t be easy and needs to be done by a garage or dealer that has done this before.
There is a couple of ways to fix this problem.
Perhaps your mercedes locks work but they open and close slowly.
Earlier this year the driver s door would occasionally not open unless i pressed the key fob repeatedly.
Apply wd 40 or equivalent product directly into the lock.
Open and close lock to recalibrate.
Have a look at yours first it could be a simple connection issue at the lock or where the wires go from the door to the main body chassis otherwise you may just be throwing away cash.
Our local mechanic couldn t identify a problem.
See also mercedes benz w204 rear door panel removal 2008 2014 c250 c300 c350 pelican parts diy maintenance article and w204 rear door panel removal google search dec.
If your car door lock actuator is not working properly a common problem is that the plastic air reservoir at the bottom of the actuator is broken or crack.
I have been quoted 1000 at the mercedes main dealer so wanted to know if anyone had any advice on what it could be before i commit to spending that much.
It seems to only play up once a month or so but now the front.
Now the rear door on the same side has the same problem.