P0411

Powertrain
Generic (SAE)
Emissions

Severity

Diagnose soon

This is an emissions device. Driveability is normally unaffected and there is no direct mechanical risk to the engine, with one exception: a valve stuck open feeds air into the exhaust continuously, which makes the upstream sensors read lean, causes the ECM to add fuel, and can overheat the catalyst.

Safe to drive: Safe to drive in most cases. Get it checked promptly if it also runs rich or the exhaust smells overheated.

Standard definition

Secondary Air Injection System Incorrect Flow

In plain English

During a cold start the computer switched on the secondary air injection system and the amount of air reaching the exhaust was not what it expected — either too little, or air arriving when none was commanded. The system exists purely to cut cold-start emissions.

Secondary air injection pumps fresh air into the exhaust ports or manifold for roughly the first minute or two after a cold start. The extra oxygen lets unburnt fuel continue burning in the exhaust, heating the catalyst to operating temperature faster and cutting cold-start hydrocarbons. The ECM verifies operation by watching the upstream oxygen sensors swing lean when the system is commanded on, or by reading a dedicated air-flow or pressure sensor on systems fitted with one. Many manufacturers use P0411 for incorrect flow in either direction — insufficient flow and flow when the system is off both land on the same code.

How the car detected it

The monitor runs once, on a genuinely cold start, inside a narrow window of coolant and ambient temperature. The ECM energizes the pump relay and commands the switching or control valve open, then measures the response. The check valve is passive — exhaust pressure holds it closed and pump pressure opens it — so it is tested for sealing and free flow, not for response to a command. An insufficient lean shift at the oxygen sensor fails the test, and so does a lean shift appearing while the system is commanded off. Because the monitor only runs under those conditions, the code will not reset until the vehicle has cooled fully — which is why diagnosis here is slow without bidirectional control.

A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.

Can I keep driving?

Safe to drive: Safe to drive in most cases. Get it checked promptly if it also runs rich or the exhaust smells overheated.
Urgency: Diagnose soon
Will it pass emissions: No
If ignored: The vehicle fails emissions testing and the monitor stays incomplete. Beyond that, a leaking check valve lets exhaust gas and condensation back into the air pump, rusting the pump internals — turning what was a valve repair into a pump replacement. A seized, water-damaged pump also blows its fuse repeatedly.
Check engine light: Solid
Clearing the light: A completed drive cycle is normally required before the monitor re-runs and the light can clear.

Likely causes

These are the causes this code can have. For the order to work through them in, see what to check first.

#	Cause	How often	Component
1	Air passages in cylinder head clogged with carbon	Very common	—
2	Air pump weak	Common	—

Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.

What to check first

In order. Each of these is cheaper or faster than what follows it, and each one can make the rest unnecessary.

Whether the pump actually runs on a cold start
Start the engine cold and listen for a loud whirring for the first thirty to ninety seconds. Silence means no pump — fuse, relay, wiring, or a seized motor — and that is the fastest branch to eliminate.
The pump fuse and relay
Air pumps draw heavy current. A repeatedly blown fuse is a strong hint the pump has taken on water and is seizing, which changes the whole repair plan.
Upstream oxygen sensor live data during the first minute of a cold start
You can watch the commanded lean shift happen or fail to happen. That confirms the ECM's complaint with no disassembly at all.
The check or combination valve and whatever controls it, vacuum or electric
A leaking check valve is a well-known failure point in these systems, and it also explains rusted pumps and carboned passages downstream.
The air injection passages, pipes and hoses for carbon and corrosion
On engines where air enters through drilled passages in the cylinder head, carbon build-up is a well-known failure, and no amount of pump or valve replacement will fix it.

How a shop diagnoses this

Read freeze frame and note the conditions when the code set
Tools Scan tool with freeze frame access
Coolant temperature and engine run time tell you whether the monitor genuinely ran and failed, or set under odd conditions.
Expected
Values inside the cold-start monitor window, confirming the test actually executed.
Observe a genuine cold start with the scan tool connected
Tools Scan tool, ears
Listen for the pump, watch both upstream oxygen sensor voltages, and note how long the ECM keeps the system commanded on.
Expected
An audible pump for roughly thirty to ninety seconds, with the upstream sensors driven clearly lean during that period and returning to normal switching afterward.
Command the system on with bidirectional control
Tools Bidirectional scan tool
Where the vehicle supports it, this lets you test on demand with a warm engine instead of waiting overnight for another cold start.
Expected
The pump runs, the control valve opens, and the upstream oxygen sensors move lean immediately.
Verify power and ground at the pump while it is commanded on
Tools Digital multimeter, wiring diagram
Back-probe the pump connector during the commanded run period.
Expected
Battery voltage at the feed and a good ground while the relay is energized. Full voltage present at a silent pump condemns the motor.
Test the check valve for sealing and the control valve for actuation
Tools Hand vacuum pump, digital multimeter
The check valve is passive, so test it for sealing rather than for response to a command: with the system off, disconnect the hose on the pump side and check whether exhaust pressure passes back toward the pump. Separately, verify that the vacuum or electrical control signal actually reaches the switching or control valve and moves it fully.
Expected
No exhaust flow back toward the pump with the system off, and a control valve that opens fully and promptly when commanded.
Check the airflow path for restriction
Tools Basic hand tools
With the pump running and the hose disconnected at the valve, confirm the pump alone moves a strong volume of air. Then check flow through the valve and into the exhaust. On systems using drilled head passages, carbon restriction shows up at this stage.
Expected
Strong airflow from the pump on its own, and a clear unrestricted path through the valve and into the exhaust.
Inspect the pump inlet and internals for water and rust
Tools Light, basic hand tools
Pumps mounted low, or fed by an intake hose that can collect water, fail from moisture ingress. Check the inlet filter and how the intake hose is routed.
Expected
A dry inlet, an intact inlet filter, and no rust particles in the pump or hoses.
Repair the specific fault, then let the monitor rerun
Tools Scan tool
Clear the code, then allow a full cold soak and perform a proper cold start. The monitor cannot run again until the engine is genuinely cold.
Expected
The secondary air monitor reporting complete with no pending or confirmed codes.

Possible repairs and what they cost

Repair	Only after you confirm	Typical cost	Who
Replace the secondary air check or combination valve	The valve leaks exhaust back toward the pump when off, or the control section fails to open fully when commanded	$150–$600	DIY
Replace the secondary air injection pump	Battery voltage and a good ground are present at the pump while commanded on, with no or clearly weak airflow output	$300–$1,000	DIY
Repair the pump relay, fuse, or wiring	No voltage at the pump connector while the system is commanded on, restored once the identified circuit is repaired	$100–$400	DIY
Replace the vacuum or electric solenoid that controls the valve	The control signal is present at the solenoid but no vacuum or actuation reaches the valve	$100–$350	DIY
Clean carboned secondary air passages in the cylinder head or manifold	Pump and valve both flow correctly when tested individually, but airflow into the exhaust is restricted	$300–$1,500	Shop
Replace corroded air injection pipes or hoses	Visible perforation, or pressurized air escaping before it reaches the exhaust	$100–$500	DIY

Pumps are the expensive part and are frequently replaced without testing the valve that destroyed them. Passage cleaning is priced almost entirely by labor and can exceed the cost of a pump on engines where the manifold or head has to come apart. Get the valve tested first — it changes what you buy and whether the repair lasts.

Common mistakes with this code

Replacing the pump when the check valve was leaking. That leaking valve is what killed the pump, and the new one dies the same way.
Testing with a warm engine. This monitor only runs on a genuinely cold engine, so a warm test proves nothing unless you have bidirectional control.
Assuming the code means no flow. Several manufacturers use it for flow when none was commanded, which is the opposite fault requiring the opposite repair.
Expecting the check valve to respond to a command. It is a passive one-way valve, so it is tested for sealing and free flow — only the switching or control valve is actuated.
Clearing the code and rechecking the same day. It needs a full cold soak before the monitor will run again.
Ignoring carbon in the cylinder head air passages on engines known for it, and replacing pump after pump instead.
Deleting or disconnecting the system. Removing or disabling a factory emissions control device is illegal under federal law, it sets a code, it fails inspection, and on some vehicles it disturbs cold-start fueling.

Components involved

Secondary Air Pump
Secondary Air Valve
Secondary Air Passages

Sources

Definition: Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
Diagnostic guidance: Written and reviewed in-house. See our editorial policy.
Review status: Reviewed

Found something wrong? Tell us — we publish corrections.

Whether the pump actually runs on a cold start

The pump fuse and relay

Upstream oxygen sensor live data during the first minute of a cold start

The check or combination valve and whatever controls it, vacuum or electric

The air injection passages, pipes and hoses for carbon and corrosion

Read freeze frame and note the conditions when the code set

Observe a genuine cold start with the scan tool connected

Command the system on with bidirectional control

Verify power and ground at the pump while it is commanded on

Test the check valve for sealing and the control valve for actuation

Check the airflow path for restriction

Inspect the pump inlet and internals for water and rust

Repair the specific fault, then let the monitor rerun