P0411: Secondary Air Injection System Incorrect Flow Detected
P0411 means Secondary Air Injection System Incorrect Flow Detected. Secondary air injection pumps fresh air into the exhaust after a cold start so the catalytic converter heats up faster. This code means air flow from the system is lower or higher than expected, measured through the upstream oxygen sensors.
Can I keep driving? Safe to drive short-term, but have it checked to avoid failed emissions or worse fuel economy.
Common symptoms
- Check engine light on
- Loud whine or no sound at cold start
- Usually no drivability change
Possible causes
- Failed air pump (often from water ingress)
- Stuck or leaking check/combination valve
- Cracked hoses or blocked air passages
- Blown fuse or faulty relay
How to diagnose P0411
- Listen for the pump running for the first minute or so after a cold start.
- Check the fuse and relay.
- Inspect hoses and the check valve; moisture inside the pump hose points to a failed check valve.
- Check the pump wiring.
What the code means, digit by digit
Generic codes have the same definition on every OBD-II vehicle (petrol cars from model year 1996 in the US, 2001 in the EU; diesels later). Manufacturers can add their own enhanced codes; those are not listed here.
Related codes
General guidance only. Fault codes describe what the engine computer saw, not which part failed: confirm with testing before replacing parts, and follow the vehicle's service information.