Hi Konrad, sorry about your problems. First, the "hi" level alarm is ,just that. Many on here have done it,and it's a simple fix. With that said, here's a bit of advice ; NEVER GO TO A DEALER, and now you know why. If you not a DIYer find a local ,independent Mercedes or German auto shop. They still charge ,$100 an hour, but a good shop won't , inflate the charges. What is the code that was given, when the "check engine" came on? If you don't have a code reader, you can go to almost any auto parts store an they will come out an test it for free. Autozone's are a national chain an very helpful in these matters. In order to help , we will need to know what that code is.