Pretty much all of the above. OBD2 was REQUIRED in 1996, however the laws governing it were the clean air act (ammendmants) of 1990 and some of the changes to transistion to it started showing up around 1993-1994. Here's some info pertaining to the EPA's clean air act as it applies to moving sources (cars, trucks, motorcycles, airplanes, etc....) Clean Air Act Why the EPA website sends to Cornell's website is beyond me....