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OBD-II codes help you find out what is wrong with your vehicle—but if you don’t know what a specific code means, how can you address the issue?

If you’re getting a P0446 trouble code on your OBD-II scanner, read on to get an idea of what this means, what may have caused it, and how you can diagnose and fix it.

What Does the P0446 Code Mean?

Code P0446, otherwise known as Evaporative Emission Control System (EVAP) Vent Control Circuit Malfunction, indicates that your car’s computer has detected (or believes it has detected) a problem with the function of the EVAP system vent valve.

mechanic pointing at a a car's purge valve
Code P0446 means the car’s computer has detected a problem with the EVAP system vent valve. The EVAP system is primarily composed of the gas tank, gas cap, vent valve, purge valve, and charcoal canister.

To help make sense of this, first, you need to know what the EVAP system is. Basically, it’s a collection of components working together to prevent fuel vapors from entering the atmosphere. Although system designs vary, typically, the primary components found within an EVAP system include the gas tank, the gas cap, the vent valve, the purge valve, and the charcoal canister.

When the engine is off, fuel vapors are stored in the charcoal canister, rather than escaping into the atmosphere. Once the engine is running and the appropriate conditions are met, the purge valve opens to allow the vapors to enter the engine, where they are burned during the normal combustion process.

The vent valve, which allows fresh air to enter the charcoal canister, is usually open. But when your car’s computer wants to check the EVAP system for leaks, it commands the electronically controlled vent valve to close, thereby sealing everything off. Then, the system can perform its self-test.

As mentioned, your car’s computer controls the vent valve (it also controls the purge valve). Additionally, the computer monitors the valve and its control circuit for problems. Code P0446 sometimes indicates that an electrical failure has been detected in either the vent valve itself or its control circuit.

While the P0446 can indicate an electrical problem on later model Fords, which, for some strange reason chooses to look at the vent valve electrical circuit to set this code, the P0446 code is highly unlikely to be an electrical concern on other makes. GMs and older Fords would set this code when the canister wouldn’t vent after the EVAP test, and in those cases, this code is far more likely to be triggered by mechanical clogging.

As described earlier, the vent valve is normally open, so an electrical problem won’t typically generate a P0446 on most platforms. The vent valve will remain mechanically open in those cases, which will vent the canister all the time – setting a different code, such as a P0455. The P0446 is more likely to be a mechanically stuck closed vent valve or a mud dobber nest in the vent. Again though, it would depend on the vehicle’s year, make, and model.

Do note that this code appears more commonly on older vehicles, usually from domestic manufacturers like GM. Dodge hasn’t listed the code for a while, and models like the Toyota Camry also haven’t listed the code since the 2007 model year.

What are the Possible Causes of the P0446 Code?

Since there are varying descriptions of the P0446 code among car manufacturers, the possible causes can differ depending on the make and model of your car.

Here are the most common causes of an EVAP System Malfunction or code P0446:

  • Malfunctioning vent control valve
  • Clogged vent valve
  • Control circuit issues (e.g., loose or damaged wiring)
  • Powertrain control module hardware or software issues (rather uncommon)

Code P0446 is set when the car’s computer believes (either correctly or incorrectly) that there’s a problem with the vent valve. Some systems use vacuum pressure readings to judge vent valve performance. As such, in some cases, parts that might surprise you can trigger the code. Examples include:

  • Failed charcoal canister
  • Faulty purge valve
  • Clogged or punctured vent hose or vent filter
  • Failing EVAP system pressure sensor

In a Lexus and Toyota, the code P0446 may point to a failing vacuum switching valve. This problem is very common to models from the two Japanese marques.

malfunction indicator on the car speedometer
The malfunction indicator light turns on if you get a P0446 Code.

What are the Common Symptoms of the P0446 Code?

Anomalies in the EVAP system often come with symptoms that you shouldn’t ignore. Below are the signs you need to look for if you get a P0446 code on your OBD-II scanner.

  • Illuminated malfunction indicator lamp or check engine light
  • Noticeable fuel odor within the proximity of the vehicle (rather uncommon)

How to Diagnose the P0446 Code

P0446 can be a serious issue. All potential causes must be looked into to come up with the correct diagnosis. Consider taking your vehicle to a professional automotive technician if you don’t have enough DIY auto repair experience and skills. However, if you still want to take a stab at the diagnosis process, the videos below can help you do it correctly.

How to Fix the P0446 Code

There are multiple reasons why code P0446 might be stored. Therefore, there isn’t a “magic bullet” fix for the issue. You’ll need to diagnose the code accurately, as outlined above, then perform any necessary repairs.

Also, keep in mind that all vehicles are different. When troubleshooting and repairing diagnostic trouble codes, you should consult the factory repair information for your application.

Repair manuals, such as those from Chilton, are useful, but an ALLDATA subscription is even better. ALLDATA has single-vehicle subscriptions for DIYers that provide detailed factory repair information.

Other Notes About Code P0446

P0446, in general, is a trouble code that’s difficult to pinpoint right away. You will need to perform a series of extensive diagnoses to get to the problem.

If you have an advanced scan tool at bay, you can use it to diagnose the P0446 code and get real-time powertrain control module data. This tool can also enable the vent and purge to turn the solenoid on and off to tell you where the leak is coming from.

Products Mentioned in this Guide

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic.

File Under : OBD-II Trouble Codes
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ChrisRinggold

That first video was great. That guy did such an awesome narrative. Exactly what I was looking for, exactly what I needed. Thanks!

CarParts.com

Hi Chris,

Wells makes some great technical videos! So glad that you found the contents of this article to be helpful!

Dale Post

I have a 09 Suzuki SX4 with 164K miles. Had a P0420, and original O2 sensors. After trying easier fixes, I replaced the O2 sensors. P0420 went away, but now I have P0134, P0138 and P2237. They both look like they are plugged in properly, so what do I do now?

Dale Post

I purchased the O2 sensors on Amazon, and they said they were an exact fit for my car. The plugs were such that they couldn’t be switched. The only other thing I can think of is that perhaps they were poor quality. They weren’t OEM.

https://www.amazon.com/gp/product/B08312NZPL/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

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