Secondary Air Injection

📖 YOUCANIC Automotive Glossary

Secondary Air Injection (SAI or AIR — Air Injection Reactor) is an emissions reduction system that pumps fresh ambient air into the exhaust manifold or exhaust ports during cold start to accelerate catalytic converter warm-up and reduce cold-start hydrocarbon emissions. The additional oxygen in the exhaust promotes combustion of unburned hydrocarbons in the hot exhaust stream (exothermic reaction), which raises exhaust temperature and helps the catalyst reach its light-off temperature (approximately 500F) faster. The system typically runs for 1-3 minutes after cold start, then shuts off once the catalyst is active. The ECU monitors SAI system operation and sets DTCs if flow is insufficient or the system fails to reduce emissions during the cold-start test window.

SAI system problems cause P0410 (Secondary Air Injection System Malfunction), P0411 (Incorrect Flow), P0412-P0419 (switching valve and relay codes), and may cause the vehicle to fail emissions testing. Common failures include a seized air pump (especially in wet climates where moisture corrodes the pump internals), stuck check valve (allowing exhaust to flow backward into the pump, destroying it), corroded or stuck switching valves, and carbon-clogged injection ports. The YOUCANIC UCAN-II can command the SAI pump to activate through Active Tests while monitoring O2 sensor response to verify airflow into the exhaust.