Drove 850 mi and had the ML washed, noticed CEL while running some errands yeasterday. Still on today. Have to drive back the 850 mi on Thrusday. Seems to run ok, should I try to get in to dealer to have it checked out before I head back? If I can't get in, I'm in Raleigh, NCheading to MI, what do you recommend if anything? Can I reset it? How?
Thanks for any and all help!

Did you add gas on your trip, you might want to check the gas cap is on tight as a starter. Will take several restarts to make it go out.

Thanks for your input. Actually the gas cap was the first thing I checked. I also looked for any disconnected vacuum lines. I did get an appointment with Leith Mercedes in Raleigh. I was given an appointment for the day following my call, they started work almost immediatly upon my arrival, and found the source of the problem in a fuel system purge valve and a cannister purge valve. The light stayed off on my return trip home to MI today. Based on my experience, I would return to Leith for service should the need arise.