Any OBD2 code reader will read OBD2 codes that throw the check engine light. They won't get into MB specific systems like climate control or ABS but still very useful to have.
The W140 used the 38 pin adapter to access most systems with an OBD2 port as a secondary connection on all 1996 or later cars after the government mandated it. The W220 was strictly OBD2. Basically any car that an icarsoft can access will be an OBD2 car as there is no (not to my knowledge) 38 pin adapter for icarsoft.
I have an AST retriever that can get into just about anything through the 38 pin diagnostic port that I use on W140's , V8 W124's , R129's and W210's.