For quite a while my Distronic on the W215 has suffered from the error message "EXTERNAL MALFUNCTION" and disengages, re-activating straight afterwards I get the same message. The fault happens mostly when temperatures are warm, usually above 10'C. Lately now it's Autumn I can switch the Distronic on without it switching off but always with a stange problem - it no longer brakes The system maintains speed and the gap by controlling the engine speed but will no longer use the brakes to slow the car down, it just ploughs on, doesn't even use the brakes going downhill . I would of thought the Distronic system would of shut itself down with such a safety critical fault and I would get the red "Visit Workshop" message. I took the car into a local Merc indy who tried to communicate with the Distronic but he couldn't get a response from the unit so I don't know if any fault codes have been generated. I've thoroughly searched the net and can find no other who this has happened to. Can anyone try and shed any light on this?