P0412Generic code

P0412 Code: Secondary Air Injection System Switching Valve A Circuit

The P0412 code means the computer found an electrical fault in the control circuit of secondary air switching valve A. Fuses, relays, connectors and wiring are the usual cause, so check those before you replace the valve. The engine runs normally, but the vehicle will not pass an emissions inspection.

Severity
Low
Can I keep driving?
Yes, no immediate risk
Estimated cost
$50 to $500
Difficulty
Medium
System
Emissions Control
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0412 code means

The secondary air system pumps air into the exhaust for the first few minutes after a cold start so the catalytic converter warms up sooner. An electric pump blows the air, and a switching valve (a vacuum solenoid or an electric valve) opens the path to the manifold.

The computer watches the control circuit from its own driver transistor. The P0412 code points to an electrical fault in that control circuit. Before you replace the component, check the fuse, the relay, the connector and the wiring, because they are the most common cause.

If the valve does not work, the air does not reach the exhaust and the catalytic converter takes longer to warm up. The engine runs the same, but the vehicle will not pass an emissions inspection. Moisture coming back from the exhaust corrodes the check valves and the passages.

Always start with the simplest things: the fuse, the relay and the connector. Then check supply, ground and signal with the component connected, using back-probes, and finally the continuity of each wire to the computer. Replace the component only if all of that checks out.

P0412 code symptoms

  • Check engine light on.
  • Usually no driving symptoms.
  • Air pump noise after a cold start is missing, or it is there when it should not be.

Likely causes of the P0412 code

  1. Damaged connector. Loose, broken or corroded.
  2. Fuse or relay blown or with worn contacts.
  3. Wiring cut or shorted between the component and the computer.
  4. Failed component. The coil, the motor or the internal electronics are damaged.

How to diagnose the P0412 code step by step

  1. Activate the component with the scan tool and see whether it responds.
  2. Check the fuse and the relay.
  3. Measure the supply at the connector. You should see battery voltage with the key on or when it is activated.
  4. Measure the resistance of the component and compare it with the manual. Check the insulation to ground too.
  5. Check the control wire for continuity and for the absence of shorts.
  6. Start the engine cold and listen for the pump. It should run for a few seconds or minutes.
  7. Activate the valve with the scan tool and check that air passes.

How to fix the P0412 code

  • Repair the connector, the wiring or the supply.
  • Replace secondary air switching valve A if it does not respond with correct supply and control.
  • Clear the codes and verify that the monitor completes.

Technical reference data

  • 12 volt solenoid, with approximate resistance of 20 to 40 ohms.
  • These are approximate values, so check the manufacturer data for your engine.

Brand-specific notes

On many vehicles moisture destroys the valves and pumps of this system, so a corroded connector or a seized valve is often the real story behind a P0412 code.

P0412 on Toyota

Frequent on Toyota vehicles, where moisture destroys valves and pumps.

P0412 on Lexus

Frequent on Lexus vehicles, where moisture destroys valves and pumps.

P0412 on Volkswagen

Frequent on Volkswagen vehicles, where moisture destroys valves and pumps.

P0412 on BMW

Frequent on BMW vehicles, where moisture destroys valves and pumps.

P0412 on GM

Frequent on GM vehicles, where moisture destroys valves and pumps.

Frequently asked questions about P0412

Can I drive with a P0412 code?
Yes. It normally does not affect driving. Repair it before the emissions inspection.
What does secondary air switching valve A do?
The secondary air system injects air into the exhaust during the first minutes after a cold start to warm up the catalytic converter sooner. An electric pump blows the air, and a switching valve (a vacuum solenoid or an electric valve) opens the path to the manifold.
Do I always have to replace the part?
No. Check the fuses, relays, connectors and wiring first.
How much does it cost to fix P0412?
Roughly $50 to $500, depending on whether it is wiring or the valve itself.
What does the P0412 code mean?
It is a generic OBD2 code for a malfunction in the control circuit of secondary air switching valve A. The computer saw an electrical problem there.
Will a P0412 code clear itself?
Only if the fault was a one-time glitch. A bad connector or a failed valve will bring the code back on the next cold start.

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