Visit this site http://www.totalcardiagnostics.com/toad for more information on Chip Tuning. The Check Engine light, which is officially called the "Malfunction Indicator Lamp" (MIL) alerts you when your vehicle's OBD II system has detected a potential emissions problem. Depending on the nature of the problem, the Check Engine lamp may come on and go off, remain on continuously or flash. Of course, none of this gives you any clue whatsoever as to what might be going on.