OBD-II Trouble Codes

P0446 Code: Evaporative Emission Control System Vent Control Circuit Malfunction

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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 was 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 often (but not always) indicates that an electrical failure has been detected in either the vent valve itself or its control circuit.

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:

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:

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.

How to Diagnose the P0446 Code

There are numerous potential causes for OBD-II code P0446. As such, diagnosis can be difficult. For an idea of how to troubleshoot the code, check out the videos below:

How to Fix the P0446 Code

Don’t believe it when somebody tells you that there’s a single, proven way to fix code P0446. Since the problem can be caused by multiple faulty parts, you will need to accurately diagnose the issue before performing any repairs.

Another important thing to remember is that vehicle models are different from each other. To avoid any potentially costly mistakes during repair, make sure to consult the factory repair information for your application.

It’s best to call your mechanic if you don’t have enough DIY knowledge to fix code P0446. You may also consider getting repair manuals such as those from Chilton or an ALLDATA subscription for 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.

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