Clear this one up real quickly, I recently had the pleasure of attending a class by a dealer technician who has run into this before. They had a late model M-class , they were doing some minor repairs and maintenance to the vehicle , one of the complaints was check engine light on . Well they pulled codes and gave coolant temp sensor code, Make a long story short they ended up replacing coolant temp sensor and to no prevaile. They ended up calling in regional rep, what it came down to was the coolant used. I didnt believe it at first either but my friend is a dealer tech in florida and he has said they have seen this several times . Besides the coolant is only 9.50 a gallon , thats almost as much as prestone or any of those other coolants. So why not just get the right stuff and save yourself the trouble.