There are three sources of automotive pollutants: crankcase fumes, exhaust gases and gasoline evaporation. The pollutants formed from these substances fall into three categories: unburnt hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx). The equipment used to limit these pollutants is called emission control equipment.
Due to varying state, federal and provincial regulations, specific emission control equipment has been devised for each. The U.S. emission equipment is divided into two categories: California and 49 States. In this section, the term "California'' applies only to vehicles originally built to be sold in California. California emissions equipment is generally not shared with equipment installed on vehicles built to be sold in the other 49 States. Models built to be sold in Canada also have specific emissions equipment, although in most years 49 State and Canadian equipment is the same.
Due to the complex nature of the modern electronic engine control systems, comprehensive diagnosis and testing procedures fall outside of the confines of this repair manual. For complete information on the diagnosis, testing and repair procedures concerning all modern engine and emission control systems, please refer to the guide To Electronic Engine Controls.