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P0412 — Secondary Air Injection Switching Valve A Circuit

Low

Quick answer

P0412 means an electrical fault in the valve that routes the air pump's output. First move: connector, wiring, then solenoid resistance — the standard circuit-code drill, on a component that lives in a wet part of the engine bay.

What it means

P0412 reports that an electrical fault in the valve that routes the air pump's output.

The secondary air system is a cold-start specialist: for the first minute or two, an electric pump blows fresh air into the exhaust so unburned cold-start fuel finishes combusting before reaching the catalytic converter. It then shuts off and does nothing until the next cold start — which is why its failures are silent except for the code and a failed emissions test.

Like every code on this site, the diagnosis below runs cheapest-first — the order exists because the cheap causes really are the common ones.

Common causes

Ordered from most to least likely.

  1. 1.

    See the diagnosis steps

    This family shares its suspect list; the steps below walk it in order of cost and likelihood.

  2. 2.

    Wiring or connector damage

    The universal suspect for any circuit-flavored code.

  3. 3.

    The component named by the code

    Condemned by measurement, never by guess.

How to diagnose it, step by step

Cheapest and most likely checks first.

  1. 1 Cold-start listening test

    First start of a cold morning: the pump's distinctive vacuum-cleaner whir should run for a minute or so. No whir = electrical side (fuse first — these pumps draw heavily and take fuses with them — then relay, then pump).

  2. 2 Inspect the check valves

    Between pump and exhaust: they must let air in and exhaust nothing out. A failed check valve breathes hot, wet exhaust back into the pump, which is the standard cause of the NEXT pump failure — replace valves with a pump, always.

  3. 3 Check the plumbing and passages

    Hoses crack near the exhaust heat, and on some engines the air passages into the heads carbon up — flow codes (P0411) with a healthy running pump point here.

  4. 4 Verify after repair

    The system only runs on cold starts, so confirmation takes a cold morning: listen for the pump, then watch that the readiness monitor completes and the code stays gone.

Parts & tools you may need

  • OBD-II scanner (code reader with freeze frame / live data)
  • Digital multimeter
  • Replacement component per the diagnosis (sensor, relay, solenoid, pump as found)

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Frequently asked questions

What does P0412 mean in plain words?
An electrical fault in the valve that routes the air pump's output. Connector, wiring, then solenoid resistance — the standard circuit-code drill, on a component that lives in a wet part of the engine bay.
The engine runs perfectly. Do I care?
The engine doesn't need this system — emissions compliance does. Cold-start pollution rises, the light stays on masking new codes, and inspections fail. It's a fix-for-the-test system, but the fixes are usually modest.
Why do these pumps keep failing?
Water — the pump's own check valves fail, exhaust moisture migrates back, and the pump corrodes from inside; some also sit low where road water reaches them. Replacing the pump WITH its check valves breaks the cycle; replacing the pump alone restarts it.