Background

One of the principle components of modern vehicle emissions control systems is the air system. This is not to be confused with the air conditioning system—the emissions air system is an entirely unrelated

group of components. The air system is also commonly known as the ‘air injection’ or ‘secondary air’ system, and we’ll use these terms interchangeably throughout this lesson.

Air injection systems become common in the 1960s and 1970s on certain vehicles to help control hydrocarbon (HC) emissions. In an engine, the ‘primary’ air system includes the engine intake and

facilitates the initial combustion process. During initial combustion, hydrocarbons are burned to create power for the engine. Because engines can’t be 100% efficient, some hydrocarbons aren’t burned completely and exit through the exhaust system. The air injection system works with the exhaust system to reduce emissions.