P0411 Secondary Air Injection Incorrect Flow
P0411 is a generic OBD2 powertrain diagnostic trouble code for secondary air injection incorrect flow. The code identifies the system or circuit the engine computer flagged, but diagnosis still depends on vehicle symptoms, freeze-frame data, and related codes.
Emissions-system codes may not feel urgent, but they can fail inspection and sometimes point to issues that damage the catalytic converter.
Common symptoms
- Check engine light
- Failed emissions readiness
- Fuel smell or exhaust smell
- Poor fuel economy
- Usually mild drivability symptoms
Likely causes
- Catalyst issue
- Secondary air fault
- Purge or vent fault
- Oxygen sensor issue
- Exhaust leak
What to check before replacing parts
Check for misfire and fuel trim codes first
Inspect exhaust leaks
Verify pump/valve operation if equipped
Review oxygen sensor data
Complete monitor drive cycle after repair
A code points at the system, not always the failed part. Add your vehicle, mileage, symptoms, and whether the check engine light is steady or flashing so the AI diagnostic can narrow the next step.