lemon law for class B

You didn't mention how long you have had it and if the other problems were eventually repaired. A check engine light most likely would not be considered a covered problem under any of the lemon laws. I believe there were other posts on one of the forums here regarding lemon laws and I believe the consensus was that the laws did not apply to motorhomes. It might be beneficial for you to just find a good mechanic familiar with Mercedes and pay for it out of your pocket. This could go on forever and it's a big inconvenience to keep dropping it off. Sometimes your just better off doing warranty repairs yourself on these units.

Good luck with it,

Nick