This is not as easy as it sounds. This is a computer controlled Benz, correct? While I am not fond of such, we are forced to deal with them. Our ML 430 did a similar thing. Turned out the computer reading machine indicated a "fault". I think our mechanic called it that. The fault was caused by me. I once opened the gas cap while the ML was running. How stupid is that??? You wouldn't believe the problems we had untill I brought it to my own tech that does the vast majority of the repairs on a real auto, the 6.3. The dealer couldn't find it when it was towed in the first time. How's that? Nor the second time , when driven in. My mechanic asked a huge number of questions. When he asked about the gas cap he just smiled.