I used this procedure after doing service D on our CDI. As I have a CDI, I don't really know where the air filter hides on the gasser.
http://www.benzworld.org/forums/w211-e-class/1427318-how-reset-after-c-service.html
http://www.benzworld.org/forums/w211-e-class/1427318-how-reset-after-c-service.html