P0411
Secondary Air Injection System Incorrect Flow Detected
- Severity
- Low
- Driving
- Drivable — book it in
The module measured secondary air flow that does not match what it commanded - too little, too much, or at the wrong moment. On a high-mileage engine the usual reason is that the air passages into the exhaust manifold have carboned up, so the pump works perfectly but the air cannot get where it is meant to go.
Possible causes
- CommonCarbon blocking the air passages into the exhaust manifold
- CommonFailed or weak air pump
- CommonFailed one-way check valve
- CommonSwitching valve stuck open or closed
- PossibleSplit or disconnected hose
- PossibleFaulty air flow or pressure sensor misreporting the flow
What you might notice
- Check engine light on
- Failed emissions test
- Rough running in the first minute from cold
- Pump noise louder or quieter than usual on a cold start
- Often no symptom the driver notices
What to check, in order
- Test from a genuinely cold start - the system does not run otherwise.
- Listen for the pump on a cold start to establish whether it runs at all.
- If the pump runs but the code persists, suspect a blockage rather than the pump. The passages into the manifold carbon up over years and are the most common cause of a flow complaint on an older engine.
- Inspect the hoses for splits and the check valve for failure.
- Check the switching valve operates when commanded.
- Do not replace the pump on this code alone. A working pump pushing air into a blocked passage produces exactly the same reading.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Auxiliary emission controls
P0400P0401P0402P0403P0404P0405P0406P0407P0408P0409P0410P0411P0412P0413P0414P0415P0416P0417P0418P0419P0420P0421P0422P0423P0424P0425P0426P0427P0428P0429P0430P0431P0432P0433P0434P0435P0436P0437P0438P0439P0440P0441P0442P0443P0444P0445P0446P0447P0448P0449P0450P0451P0452P0453P0454P0455P0456P0457P0458P0459P0460P0461P0462P0463P0464P0465P0466P0467P0468P0469P0470P0471P0472P0473P0474P0475P0476P0477P0478P0479P0480P0481P0482P0483P0484P0485P0486P0487P0488P0489P0490P0491P0492P0493P0494P0495P0496P0497P0498P0499