What are Tier I emissions standards?
When the Clear Air Act was amended in 1990 it created two classes of emissions standards for light duty vehicles in the United States. Tier I standards began going into effect in 1994 and were in full use by 1997. All new vehicles with a GVWR of under 8,500 lbs. were subject to the standards, although subcategories within created different specific requirements based on vehicle type.
