P0411: Secondary Air Injection System A Incorrect Flow Detected
What to do
Driveable, and will fail an emissions test. If a pump is being replaced, ask whether the check valve is being replaced with it — fitting a pump behind a failed check valve is how the same repair gets done twice.
What this code means
Air is reaching the exhaust, but not in the quantity expected — too little, or at the wrong moment. The module infers flow from the change in the upstream oxygen sensor reading when the pump runs: injected air makes the exhaust appear lean, and the size and timing of that swing is the measurement.
The failure that dominates in practice is the check valve. It sits between the pump and the exhaust and exists to stop hot exhaust gas travelling back into the pump; it lives in exhaust heat and carbon, and when it seizes partially open the pump is destroyed by the gas it was meant to be protected from. Two consequences follow. First, a failed pump on this system is frequently a symptom rather than the cause, and replacing it without the check valve buys a second failure. Second, a car that has been standing or driven only on short journeys accumulates condensate in the pump, and freezing weather finishes it.
Likely causes
Start here
- Seized secondary air check valve · moderate
- Carbon-blocked secondary air passage · moderate
- Failed secondary air injection pump · moderate
Less common
- Faulty secondary air switching valve · moderate
- Split or disconnected air hose · easy
Rare
- Faulty oxygen sensor · easy
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P0411.