The OBD connection is under the hood on the passenger side near the windshield. It is a small box with a cover that opens with numbered pin connections, a button, and a red LED. The best tool to use is a MB HHT or MB STAR system with HHT connector. There are a few other tools which will communicate also but they are pretty expensive (Snap-On Modis, Autoboss, Autel Maxidas, etc.). Contact me once you retrieve the codes and I can give you the description(s).
I have the factory MB tools at the shop and would be happy to help if you get stuck.
James Wallace EuroAsian Garage Seatac, WA www.euroasiangarage.com