SAI Pump

📖 YOUCANIC Automotive Glossary

The SAI Pump (Secondary Air Injection Pump) is the component that physically delivers fresh air into the exhaust system during cold starts to help the catalytic converter reach operating temperature faster. Modern SAI pumps are electrically driven and activated by the ECU through a relay for 1-3 minutes after cold start. Older systems used a belt-driven mechanical pump that ran continuously with an air switching valve directing airflow. The electric pump draws ambient air through an inlet filter, pressurizes it, and delivers it through a one-way check valve and switching valve into the exhaust manifold or cylinder head exhaust ports.

SAI pump failure is common, especially on vehicles driven in humid or wet environments — moisture entering the pump through the intake filter causes internal corrosion and eventual seizure. A seized pump draws excessive current that blows the pump fuse or relay, setting P0410/P0418 codes. A pump that runs but delivers reduced airflow sets P0411. DIYers can test the pump by energizing it directly with 12V — it should spin freely and produce noticeable airflow. Also inspect the check valve — a failed check valve allows hot exhaust gases to flow backward into the pump, melting plastic components and causing rapid failure. Replacement pumps should be installed with a new check valve.