P0411 to P0414: secondary air injection flow and valve circuit

Secondary air injection exists to solve one narrow problem: a catalytic converter does nothing until it is hot, and the first minute after a cold start is when a petrol engine emits most of its pollution.

The system pumps fresh air into the exhaust manifold immediately after start-up. That extra oxygen burns the rich cold-start mixture in the exhaust, heating the catalyst faster.

It runs for roughly 30 to 90 seconds, once per cold start, and then does nothing for the rest of the day.

Related: secondary air injection P0410 diagnostics.

Code	Meaning
P0410	Secondary air injection system malfunction
P0411	Incorrect flow detected
P0412	Switching valve A circuit
P0413	Switching valve A circuit open
P0414	Switching valve A circuit shorted

Why you will not notice the fault

The system operates for under a minute, at a moment when you are pulling away and not paying attention. It has no effect on power, economy or driveability.

The only consequences are emissions and a warning lamp — plus a failed emissions test, which is how most people discover it.

That invisibility is also why the fault is usually well advanced before it is found.

The corrosion problem

This is the defining failure of the system, and it is self-inflicted by the design.

Combustion produces water. Cold exhaust condenses it. The secondary air passages connect a pump to the exhaust manifold, and water finds its way back into them.

Over years, that water rusts:

• The check valve, which is supposed to stop exhaust gas reaching the pump.
• The passages in the cylinder head, which block with rust and carbon.
• The pump itself, once the check valve fails and lets exhaust gas through.

Once the check valve fails, the pump has a limited life. Replacing a pump without replacing the check valve is a repair that fails again.

What each code points at

P0411 — incorrect flow

The ECU expected the oxygen sensor to read lean while the system ran, and it did not — or it read lean when the system was supposed to be off.

Causes: blocked passages, a failed pump, a stuck valve, or a leaking check valve letting exhaust into the system continuously.

P0413 and P0414 — valve circuit

Electrical. Open or shorted circuit to the switching valve, or a failed driver.

Check the connector, the fuse, the relay and the valve resistance in that order. On many vehicles the pump is fed through its own relay: fuses and relays basics for owners.

Testing it, which is time-limited

The system only runs after a genuine cold start, so the test window is narrow.

1. Leave the car overnight.
2. Start logging before you start the engine.
3. Start the engine and listen — a working pump makes a distinct loud whirr for 30 to 90 seconds.
4. Watch the upstream oxygen sensor. It should swing lean while the pump runs, because the extra air reaches it.

Observation	Meaning
Loud pump noise, sensor reads lean	System working
Pump audible, sensor unchanged	Passages blocked or valve stuck closed
No pump noise	Electrical, relay, or a dead pump
Sensor reads lean without the pump	Valve stuck open — exhaust leak into the system

You get one attempt per day. Once the engine is warm, the system will not run again until it fully cools.

O2 sensor waveform analysis.

The rough cold idle connection

A valve stuck open lets air into the exhaust continuously. The upstream oxygen sensor reads lean, the ECU adds fuel to compensate, and the engine runs rich and rough when cold.

If you have a cold-idle complaint alongside a P041x code, they are one fault: rough idle when cold.

Is it worth fixing?

Honest answer: it depends where you are.

The system has no effect on how the car drives. But:

• It will fail an emissions test in markets that check the lamp or read codes: OBD codes and MOT emissions test.
• The lamp masks other faults. With the light already on, you will not notice the next code.
• A stuck-open valve genuinely affects running, as above.

The repair cost varies enormously by engine — some pumps are accessible, some head passages require significant dismantling to clear.

Sequence

1. Cold start with logging running. One attempt per day.
2. Listen for the pump.
3. Watch the upstream sensor for the lean swing.
4. Check fuse, relay and valve circuit if the pump is silent.
5. Check the check valve before replacing a pump.
6. Expect blocked passages on any high-mileage engine with this code.

Pair an ELM327 adapter, open the free tier of the app and record the first ninety seconds of a cold start. That recording contains the entire diagnosis for this system.