What does the secondary air injection system do?

The secondary air injection system is designed to inject additional air into the exhaust system, specifically during cold engine operation or during certain conditions when additional oxygen is needed. By introducing air into the exhaust system, the secondary air injection system helps complete the combustion process for unburned fuel in the exhaust. This process significantly contributes to reducing harmful emissions, such as hydrocarbons and carbon monoxide, that can be present in the exhaust gases when the engine is operating at lower temperatures.

Moreover, while the injection of air primarily occurs in the exhaust system, this action leads to improved oxidation of the remaining unburned fuel, helping to lower overall exhaust emissions. Therefore, the core function of the system is to inject air into the exhaust, aligning with its purpose to enhance emissions control during specific operating conditions.