The purpose of this system is to prevent excessive amounts of Carbon Monoxide (CO), Hydrocarbon (HC) and Nitrous Oxide (NOx) emissions from being given off with the normal engine exhaust. The methods employed to accomplish this purpose have been revised and varied over the past several years in order to meet stricter government standards, while at the same time maintaining or improving vehicle performance. From 1970 Subaru has made a number of changes in its exhaust emission control system. Some changes are minor, others involve adding or eliminating major components.
There are four basic systems within the Subaru exhaust emission control system. Despite variations in terminology from year-to-year, they can be classified as: engine modification system, air injection (suction) system, exhaust gas recirculation system and on selected models, a catalytic converter system or a three-way catalyst attended with an Electronically Controlled Carburetor (ECC) system.