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  • On-board diagnostics (OBD) can log a P0412 if the vehicle computer detects a problem with the secondary air injection (SAI) system’s “A” circuit.
  • Wiring issues, a damaged SAI switching valve, and a clogged or disconnected vacuum hose can trigger a P0412 code.
  • If this code is present, your vehicle could exhibit symptoms like increased tailpipe emissions and a rich air-fuel mixture.

The secondary air injection (SAI) system forces fresh air into the exhaust system to help in the oxidizing process happening in the exhaust manifold or catalytic converter. It reduces HC and CO emissions by providing fresh air into the exhaust system.

A typical SAI system has a check valve that protects other components from reverse exhaust flow, as well as various air management valves. Once the powertrain control module (PCM) detects an issue with the SAI system, it will log a P0412 code.

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What Does the P0412 Code Mean?

Diagnostic trouble code (DTC) P0412 stands for “Secondary Air Injection System Switching Valve ‘A’ Circuit.”

The SAI system operates during cold engine startup, pumping fresh air into the exhaust and combining it with the post-combustion HC and CO to provide secondary oxidation. This process converts the residual HC and CO to water vapor and CO2. A switching valve is used to allow air to flow from the SAI pump to the exhaust stream.

Problems can arise with the switching valve and related components. Once this happens, on-board diagnostics will log a P0412 code.

Note: The definition of code P0412 might be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

car exhaust showing stainless exhaust pipe
The SAI system operates during cold engine startup, pumping fresh air into the exhaust and combining it with the post-combustion HC and CO to provide secondary oxidation.

What are the Common Causes of the P0412 Code?

What are the Common Symptoms of the P0412 Code?

How to Diagnose the P0412 Code

DTC P0412 is a generic powertrain code that vehicles equipped with an OBD-II system can log. But despite being a common trouble code, its steps for diagnosis and repair can vary from one vehicle to another.

See also  P0431 Code: Warm Up Catalytic Converter, Bank 2—Efficiency Below Threshold

If you’re not familiar with the process of diagnosing trouble codes, it’s a good idea to bring your vehicle to the nearest auto repair shop and have a trained professional do the job for you. Otherwise, you can go ahead and do it yourself.

To help you out, we’ve gathered a couple of videos to give you an idea about what the process might involve.

How to Fix the P0412 Code

There’s not a single solution to fix every trouble code in the book. The steps for fixing DTC P0412 can differ, depending on your vehicle’s year, make, and model.

If you’re not confident with your DIY skills yet, you can always have a certified mechanic do the job for you to ensure that the right steps are followed. But if you think you have the skills and technical knowledge to do it, then you can go ahead and fix the problem on your own.

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Before you start, make sure you have the right tools and repair guides. Manuals like those from Chilton or an ALLDATA subscription contain vehicle-specific repair information, so you might want to check those out before proceeding.

About The Authors
Written By Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Contact Center Manager and Technical Reviewer at

William “Bill” Guzenski has produced hundreds of how-to videos for the automotive community. He’s an ASE Certified Master Automobile Technician, and is affiliated with the Specialty Equipment Market Association (SEMA). He loves attending race events and car shows throughout the country, as well as traveling in his 40-foot motorhome, exploring abandoned mines and ghost towns.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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