Omegabenz, there is NO SUCH THING as a NOx sensor. There is, however, a KNOCK sensor. I believe myarmar's post will corroborate the information in my previous post. I consider myself a "seasoned tech" (14 years with MB, and counting ) so I'm not making this up. The information in your original post is inaccurate, and I felt obligated to correct you. Sorry. The Forum members expect to hear OPINIONS, but sometimes only the FACTS will do. Have a nice day.