this is a common problem. I had this happen to my ML320 (same engine as a Crossfire). It is not a big deal to fix yourself if you are out of warrenty. You can get the sensor at at a import parts store cheaper than a dealer. It is located at the rear of the engine at the top near the bell housing. Unclip it and remove two screws which if I remember right are torx. Pop in the new one and you are back on the road in about 15 minutes. Keep this in mind if a dealer tries to charge $ hundreds.