Okay, I'm not trying to be a wise ass or anything, but I'll relate a somewhat embarassing story to you. I had a light go on on my dash a few months ago (two weeks after purchasing), it looked like a cross-section of an engine with an exclamation point in the middle. This is exactly what a check engine light looks like on every GM product that I have ever owned. I hunted for codes with the push button LED diagnostic center and got nothing. Of cours it turns out that this symbol meant that I had an exterior bulb burned out (GM would never think of warning the driver of this), and only then did I realize that the check engine light on MB actually says "check engine". I only mention this because you said it came on "tonight", and the exterior bulb warning light only comes on when the headlight switch is switched on. My apologies if this post is obvious; just hoping that I'm not alone in being the most ignorant member on the board (ignorance loves company!)!! Good luck!
1995 E320 wagon