THREE-WAY -- Also known as Oxidation/Reduction. This converter, together with electronic engine controls, both reduces and oxidizes. It reduces nitrous oxides into nitrogen and oxygen. And, it oxidizes hydrocarbons and carbon monoxide. Many vehicles required three-way emission control beginning with 1980 in California and 1981 for the other 49 states. Use on computer controlled vehicles.

THREE-WAY + OXIDATION -- This type performs the same functions as the other two. But it's like two converters in the same body. Typically, this unit has an air tube connection. Use on computer controlled vehicles and/or vehicles with air pumps on the engine.

OXIDATION -- This type of converter oxidizes unburned hydrocarbons and carbon monoxide into water and carbon dioxide. Use on all other models.