Faulty or seized secondary air pump, or a pump that is blocked or worn; Stuck, leaking or clogged secondary air check valve or combi valve, often from moisture or carbon build-up; Blocked or restricted air injection pipes or ports in the cylinder head or exhaust manifold; Faulty air switching or vacuum/solenoid valve, or a vacuum supply leak or split hose; Wiring, connector or relay fault, or a blown fuse in the pump or valve circuit; Faulty air mass, pressure or oxygen sensor giving a wrong reading during the test; Exhaust leak upstream of the oxygen sensor that upsets the test result.

P0411

AIR System A Incorrect Flow Detected.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
4: AreaAuxiliary emission controls
11: FaultThe specific fault in that area

What it means

P0411 means the secondary air injection (AIR) system has not moved the expected amount of air when the control unit tested it. The test normally runs shortly after a cold start, when the pump switches on and the control unit checks the oxygen sensor or pressure sensor response against what it expects. If the reading shows too little or too much air, the code is stored and the warning light usually comes on.

Symptoms

Engine warning light on
Whining, buzzing or no noise at all from the air pump after a cold start
Slightly higher cold-start emissions or a rough cold idle
Failed emissions test
Reduced performance or limp mode on some vehicles

Possible causes

Faulty or seized secondary air pump, or a pump that is blocked or wornlikely
Stuck, leaking or clogged secondary air check valve or combi valve, often from moisture or carbon build-uplikely
Blocked or restricted air injection pipes or ports in the cylinder head or exhaust manifoldpossible
Faulty air switching or vacuum/solenoid valve, or a vacuum supply leak or split hosepossible
Wiring, connector or relay fault, or a blown fuse in the pump or valve circuitpossible
Faulty air mass, pressure or oxygen sensor giving a wrong reading during the testrare
Exhaust leak upstream of the oxygen sensor that upsets the test resultrare

How to diagnose

Read the stored and pending codes and the freeze frame data, noting engine temperature and conditions when the fault set. Check for related codes such as pump circuit or oxygen sensor faults.
Check the fuses and relay for the air pump and valves, then inspect the wiring and connectors for damage, water ingress and corrosion.
Listen to the pump on a cold start. No noise suggests a power, relay or pump fault, and an unusually loud noise suggests a worn pump.
Inspect the air hoses, pump inlet filter and vacuum lines for splits, blockages, water or loose connections.
Using a scan tool with bi-directional control, run the air pump and valves, and check for correct operation and live sensor response. The procedure depends on the model.
Check the pump supply voltage and earth while it is commanded on.
Test the check valve or combi valve for free movement, leakage and blockage, and check the air passages for carbon build-up or water damage.
Inspect the exhaust for leaks near the injection point or sensors, and check sensor data against the manufacturer's specification for your model.

How to fix

Replace the secondary air pump if it has failed, seized or is blocked.
Replace a faulty check valve or combi valve, and clear any water or debris from the system.
Clean or clear blocked air injection pipes and passages, following the manufacturer's procedure.
Repair or replace damaged vacuum hoses, solenoid valves or switching valves.
Repair wiring or connector faults and replace blown fuses or faulty relays, finding out why the fuse blew.
Repair exhaust leaks or replace a faulty sensor only once it has been confirmed as the cause.

Can I keep driving?

Low severity

The car can normally be driven for a short time as this fault mainly affects cold-start emissions. Book it in soon, as water or debris in the system can damage the pump or valves, and some models may limit performance.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.