P0411AIR System A Incorrect Flow Detected
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- After a cold start the secondary air (AIR) pump blows fresh air behind the exhaust valves so that unburnt fuel burns off and the catalyst heats up faster; a shut-off valve opens the path and stops exhaust from flowing back. P0411 means the measured air flow does not match the expected value. Passive systems judge it from the oxygen sensor or fuel control (Saab 900: less than 12 points of correction within 12 s). GM measures actively with a pressure sensor between pump and valve and compares it with a model while pump and valve are on – from 2018 a deviation above 5.0 kPa or below −4.9 kPa sets the code, MIL after two trips. The test needs a cold engine after a long stop, so short warm trips do not complete it.
- What you may notice
- Check engine light on
- Secondary air readiness not set (emission test)
- Pump silent after a cold start, or unusually loud
- Driving normal, higher cold-start emissions
- Likely causes
- LikelyPump weak or failed (water, filter debris)
- LikelyCombination valve partly stuck or check valve faulty
- PossibleHoses blocked, leaking or off; ducts in the head carboned up
- RarePressure sensor port blocked or sensor drifting (pressure-sensor systems)
- RarePump relay or supply with contact resistance
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €80 – €1,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.