Interior pictures would help, especially if there is an internal emergency release handle.

Looks like this is an electric security / central locking system.
We Need a better DIY on this known common issue on w203's......
Here is the best I could find on the net.

http://mbworld.org/forums/5291493-post20.html

http://www.google.com/search?q=171-750-00-85&rls=com.microsoft:en-us&oe=UTF-8&startIndex=&startPage=1&rlz=&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=QWUdUc7rLcH1ygGttoCIDg&biw=1251&bih=713&sei=cWUdUbvuMpKFyQHAqYCoDg

Trunk button on the driver door zero function = FAILED.

Insert the blade key into the trunk lock turn it counter clockwise and hold it in that position while trying to open the trunk handle = FAILED, several hundred attempts.

Desperation = Not tried yet, and would prefer to avoid this...
If that fails you can break the left rear tail light and work your way up to the interior trim, then break the trim and directly pull the cable.


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