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  • The P0418 code stands for “Secondary Air Injection (SAI) System Control ‘A’ Circuit,” which means the powertrain control module (PCM) detected that the SAI control circuit’s voltage signal differs from the expected value.
  • A bad SAI pump relay, a broken SAI pump, and wiring or connector issues are common causes of the P0418 code.
  • An illuminated check engine light and the vehicle being stuck in “limp mode” are common symptoms of the P0418 code.

Modern vehicles are composed of different systems that work together to keep your ride running smoothly. The role of the secondary air injection (SAI) system is to supply fresh air to the exhaust stream to reduce emissions. On many vehicles, this system also helps the catalytic converter get to its operating temperature when the engine starts.

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P0418 is a trouble code related to a malfunction in the secondary air injection system control circuit. Read on to learn more about it.

What Does the P0418 Code Mean?

Diagnostic trouble code (DTC) P0418 stands for “Secondary Air Injection System Control “A” Circuit.” The A designation can mean it’s the only circuit or its specific circuit out of multiple circuits in the system.

How the SAI System Works

Black Secondary Air Injection Pump for Car
The SAI system is equipped with either a belt-driven pump or an electric pump.

Some vehicles have an SAI system to reduce harmful emissions through oxidation. This system is equipped with either a belt-driven pump or an electric pump. This pump draws ambient air, compresses it to some degree, and routes the pressurized air into the exhaust manifolds or catalytic converter. Your vehicle’s powertrain control module (PCM) controls the valves in the system to regulate and distribute air correctly.

The PCM monitors fluctuations in air pressure using input voltage signals. Once the PCM detects a voltage signal from the SAI control circuit that’s not according to what’s expected, it will trigger the P0418 code.

Note: The definition of code P0418 could be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What Are the Common Causes of the P0418 Code?

  • Bad SAI pump relay
  • Wiring and/or connector issues
  • Malfunctioning SAI pump
  • Blown SAI system fuses
  • An issue with the PCM, such as software in need of an update
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What Are the Common Symptoms of the P0418 Code?

car check engine light illuminated clear view
An illuminated check engine light is a common symptom of the P0418 Code.

Although addressing the P0418 code doesn’t always come with great urgency, it is still important to do so. Remember that exhaust emissions contribute to pollution in the atmosphere. Some of the common symptoms attributed to the code include:

How to Diagnose the P0418 Code

DTC P0418 is a generic powertrain code, which means it can be logged on various vehicles. Keep in mind that the steps for diagnosis and repair can vary depending on the specific vehicle you own. For instance, diagnostic procedures for a P0418 code in a Toyota Tundra can be different from that for a P0418 code in a VW Jetta.

If you’re not confident with your DIY skills yet, it’s a good idea to bring your vehicle to a mechanic to ensure that the right steps are being followed.

Here is a video that shows what the process might involve:

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How to Fix the P0418 Code

Attempting to fix a P0418 code isn’t easy—especially if you’re not equipped with the right tools and technical knowledge. If you’re not familiar with exhaust systems and vehicle repair, you should take your vehicle to the nearest shop and have a certified mechanic do the job for you. If you plan on doing the job yourself, make sure to do your research and read the manual before doing any repair work. Guides like those from Chilton or an ALLDATA subscription come with vehicle-specific repair information that will make the job easier.

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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