I am sure that you can not use the OBD connector to reset limp mode. You need to the 38 pin round connector under the hood. You will need a Mercedes Cartridge up to and including the model year of your car. The generic Euro cartridge is only used to connect to your cars obd, you don;t need that.
Besides the cartridge you need the cable that connects to the 38 pin connector (MB-1 connector pn MT2500-62). It has the slot for the personality key.