EN

Severity: Low Code type: Generic (all makes)

P0411 Code: Secondary Air Injection System Incorrect Flow Detected

The air pump runs at cold start, but the right amount of air isn't reaching the exhaust.

At a glance

Severity: 2/5 – Low2/5

Severity: Low

Meaning
Secondary Air Injection System Incorrect Flow Detected
System
Emission Controls · Powertrain
Safe to drive?
Yes, short term
Typical repair cost
$60–$2,800
DIY difficulty
Moderate

P0411 narrows the secondary air problem down compared with the general P0410: the ECU switched the system on but measured the wrong amount of air arriving in the exhaust. On most engines 'wrong' means too little, judged by how far the upstream O2 sensors swing lean during the cold-start test or by a secondary air pressure sensor. The pump itself frequently still runs, so the restriction or leak sits further down the path: carbon-choked passages in the cylinder head, a rusted or stuck check valve, a split hose, or a control valve that doesn't open fully. Because the passages in the head are the hardest part to clean, confirming exactly where the air stops saves a lot of labor.

Can I keep driving? Safe to drive. The system only matters for the first minute or two after a cold start, so you won't notice any difference once the engine is warm, but you won't pass an emissions test until it's fixed.

How to read P0411

How to read P0411P10243114
  1. P Powertrain
  2. 0 Generic (SAE)
  3. 4 Auxiliary emission controls
  4. 11 Specific fault

Symptoms

  • Check engine light, usually appearing after cold starts
  • Pump is audible at cold start, yet the code keeps coming back
  • Hissing or puffing noise from a leaking air hose at cold start
  • Slightly rougher running in the first minute on some engines
  • Secondary air monitor incomplete or failed on an emissions test

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Carbon blocking the air injection passages in the cylinder head or exhaust manifold 30%
  2. Check valve (combination valve) rusted or stuck closed 25%
  3. Split, disconnected or melted hose between pump and valves 15%
  4. Pump running but worn, delivering too little air 12%
  5. Vacuum control solenoid or vacuum line preventing the valve from opening 10%
  6. Slow upstream O2 sensor or faulty secondary air pressure sensor misjudging the flow 8%

Diagnosis step by step

Diagnostic flow: P04111Confirm the pump runs and moves air2Test the check valve3Check the vacuum signal to the valve4Prove the passage into the exhaustis open5Compare O2 sensor response duringthe test6Clean passages and retest

  1. Confirm the pump runs and moves air

    Command the pump on with a scan tool, or do a cold start, and disconnect the hose at the check valve. You should feel a strong, steady blast of air; a weak puff points to a tired pump or a leak between pump and valve.

    Tools: OBD-II scanner, Screwdriver

  2. Test the check valve

    Remove the check valve and blow through it. It should pass air only toward the exhaust and only when opened (by vacuum on pneumatic valves or by air pressure on passive ones); rust, soot or a valve that won't open is your restriction.

    Tools: Vacuum gauge, Flashlight

  3. Check the vacuum signal to the valve

    On vacuum-operated check valves, tee in a gauge and command the system. Vacuum should appear at the valve within a second; if it doesn't, trace the line back to the control solenoid.

    Tools: Vacuum gauge, OBD-II scanner

  4. Prove the passage into the exhaust is open

    With the check valve removed, feed smoke or low-pressure air into the port on the head or manifold. It should flow freely and exit at the tailpipe; heavy resistance means carbon-blocked passages that need cleaning.

    Tools: Smoke machine, Flashlight

  5. Compare O2 sensor response during the test

    Graph both upstream O2 sensors on a cold start with the pump on. They should swing clearly lean within a few seconds; on a V engine, one bank reacting and the other not points to a blocked passage or valve on the lazy side.

    Tools: OBD-II scanner

  6. Clean passages and retest

    Blocked ports can often be cleared through the check valve opening with a long drill bit or wire turned by hand, followed by vacuuming out debris. Severe blockage deep in the head may require removing the intake or head, so confirm the flow before and after cleaning.

    Tools: Gloves, Flashlight

Where the parts are

Exhaust: catalytic converter and O2 sensors (Bank 1 / Bank 2) – P04111212345
Exhaust: catalytic converter and O2 sensors (Bank 1 / Bank 2)
  1. 1Upstream O2 sensor
  2. 2Catalytic converter
  3. 3Downstream O2 sensor
  4. 4Diesel particulate filter
  5. 5Turbocharger

Repair options & costs

RepairDIY?Estimated cost
Replace split or disconnected air hose Yes $60–$250
Replace check (combination) valve No $150–$450
Clean blocked secondary air ports No $300–$900
Replace secondary air pump No $350–$950
Cylinder head removal to clear deep blockages No $1,200–$2,800

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Notes by brand

BMW

BMW inline-sixes of the M54 family (for example in the E46 3 Series, E39 5 Series and E53 X5) are known for P0411 when the secondary air passages in the cylinder head clog with carbon. Check valve and pump are cheaper to test first, but many cases come down to the passages.

Volkswagen

The 1.8T 20-valve engine in the Golf/Jetta IV and Passat B5 is known for P0411 from a sticking combination valve and carbon-choked ports behind it. Check the vacuum line to the combination valve as well, since it becomes brittle with age.

Audi

Audi A4 and TT models with the 1.8T share the same weak spots: the combination valve and the air passages in the head. Carbon can be cleared through the valve port in many cases before resorting to head removal.

Field data

Chevrolet 7 Cruze, Equinox, Impala
Subaru 2 Impreza, Wrx

Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.

Emissions / smog test impact

Will fail

An active P0411 fails OBD-based smog checks. Because the secondary air monitor only runs on a genuine cold start, allow several cold mornings after the repair so the monitor reads 'complete' before the retest.

Frequently asked questions

The air pump runs. Why do I still get P0411?

P0411 is about flow reaching the exhaust, not whether the pump spins. A stuck check valve, a leaking hose or carbon in the ports can stop the air even with a healthy pump.

Can I clean the passages without taking the head off?

Often yes. On many engines the passages can be reached through the check valve mounting hole and cleared with a long bit or wire, turned by hand, then vacuumed out. Only heavily blocked internal passages need the head removed.

How is P0411 different from P0410?

P0410 is the general 'system doesn't work' code and often means the pump is dead. P0411 means the system ran but the airflow was wrong, which points further down the path to valves, hoses and passages.

Sources