P0411 – Secondary Air Injection System Incorrect Flow Detected

What does P0411 mean?

The secondary air injection system is not flowing the amount of air the computer expects. This system pumps fresh air into the exhaust during cold start to help the catalytic converter reach operating temperature faster and reduce startup emissions.

What causes P0411?

Listed from most to least common:

1. 1Failed secondary air injection pump
2. 2Carbon buildup blocking air passages
3. 3Stuck or failed check valve
4. 4Failed switching/diverter valve
5. 5Damaged hose or wiring
6. 6Water intrusion damaging the pump

Code breakdown

Common symptoms

• Check engine light on, typically appearing shortly after a cold start
• Loud noise from the air pump on startup, or no pump noise at all
• Normal drivability
• Failed emissions test

How to diagnose

1. 1Listen at cold start — the pump should run audibly for roughly 30–90 seconds. Silence suggests pump or relay failure.
2. 2Check the pump fuse and relay.
3. 3Inspect hoses for cracks or disconnection.
4. 4Test the check valve, which commonly fails and allows exhaust back into the pump.
5. 5Inspect the air injection passages in the exhaust manifold for carbon blockage.
6. 6Command the pump on with a scan tool and verify operation.

No meaningful drivability impact, but the vehicle will fail emissions testing and repairs on some models can be expensive.

Common fixes and estimated costs

Costs are rough US estimates including parts and labor. Actual pricing varies significantly by vehicle, region, and shop rates.

Good to know

A failed check valve often destroys the pump by letting hot exhaust and moisture back into it. If you are replacing the pump, replace the check valve at the same time or the new pump may fail the same way.

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