I took my 240D to the mechanic today. During the conversations about racing, skydiving, NASCAR, etc., the comment "check engine" light came up. What I learned was that when you "over-fill" the fuel tank, (at least on the newer MBs) you will get that "check engine" light. He said that when pumping fuel, stop as soon as the pump kicks off. Because there's a gadget that measures the amount of air(?), and fuel and when you keep trying to put more fuel into it, you mess up that electronic gadget's reading. So, he says to STOP PUMPING fuel as soon as the PUMP CLICKS OFF and you will not get that (faulty) "check engine" light. He said he learned that himself. Also several other 'goodies' but not pertaining to MB's.
You who are experiencing this "check engine" may want to observe this with your vehicle, assuming that in reality you don't need to have the engine checked.
Helen