I've done an exhaustive search on this code. My friend's E320 wagon has the CEL illuminated. I pulled up a code 17. It has something to do with one or more control modules not communicating with the other(s). The problem is I can't seem to find out what that exactly means, a new control unit somewhere? When the code is cleared, it returns after a few hours/days of driving. The car drives as beautifully as ever and fuel mileage is not effected. If anyone knows what that code means, that would help greatly - it seems to be very common on E420s I've read, not only code 17, but the fact that one module has stopped communicating with another.

The second VERY interesting piece to this puzzle (and I'm hoping this will bring forth an answer) is that while the CEL is illuminated with the engine running, it remains illuminated for about 45 seconds or so AFTER the engine is turned off and the key is in hand. Anyone ever heard of that with a CEL before???