A very common trouble code with the Toyota Mirai is the P0446 code. This trouble code references a number that is given to you when you plug your Mirai into a OBDII scanner. P0446 Indicates that there is a fault in the evaporative emission control system. It often appears with other codes, such as P0420, P0441, or P0440.
P0446: Evaporative Emission Control System → Vent Control Circuit → Malfunction
P0446 is normally not an immediate threat to the drive-ability of your vehicle. Certainly anytime the service engine soon light is on, it’s good to deal with it as soon as possible though. It is often accompanied by P0442. P0420 is another common trouble code that often accompanies P0446.
Toyota Mirai P0446 OBDII Code Symptoms
P0446 code will typically not be accompanied by any noticeable symptoms. The service engine soon light will come on, but that is usually about it. You might (not very likely) notice a slight decrease in fuel economy. P0446 may also cause a slight gas smell. This is due to it being related to the system that deals with fuel vapors.
Toyota Mirai P0446 Meaning
P0446 is a universal OBDII trouble code. This means that regardless of which make or model of vehicle, the code will mean the same thing (Mirai or not). The code technically stands for:
Evaporative Emission Control System Vent Control Circuit Malfunction
The EVAP system captures all fuel vapor from the fuel tank and sends them to the engines intake in order to be ignited in the normal combustion process. When the EVAP control system vent control circuit no longer responds to the ECU, it will throw the P0446 OBDII Code, and the service engine soon light will illuminate.
Mirai P0446 Trouble Code Causes
There are many things that can cause the P0446 trouble code to trigger in your Toyota Mirai. Here are the most common problems that will throw the code:
- Vapor Canister Purge Valve– One of the most common causes of the P0446 code is the vapor canister purge valve. It’s really easy to replace. There are a few clips that you need to find and remove.
- EVAP System Hose– The hose that carries the fuel vapor from the fuel tank to the intake manifold can begin to leak. This will cause the P0446 code. Look for either a tear or hole in it.
- Faulty Charcoal Canister– The charcoal canister is often the cause of P0446.
- Fuel Tank Sending Unit– It is possible for the fuel tank sending unit to go bad. This can mess with line pressure and throw the code.
- Fuel Cap– A bad fuel cap can cause the code to be thrown for sure. Often, you’ll get a message informing you that the fuel cap is off even when it is on. If you are getting that message, plus a P0446, it may save you a ton of time and money to replace the fuel cap and see if it goes away.
- Fuel Filler Neck– There is often a gasket where the fuel filler neck connects with the gas tank. This gasket can dry out, especially with vehicles that spend their time in dry climates. When it dries out, the fuel tank can’t hold pressure anymore.
P0446 Diagnosis- Toyota Mirai
A mechanic has a wide range of instruments at his disposal to diagnose what would be causing the P0446 in your Toyota Mirai. Here are the most common things that are done to diagnose the code:
- The mechanic will typically check to see if there are any other trouble codes. The more trouble codes there are, the easier it can be to diagnose a problem. That’s because when they appear together in certain combinations, there will often only be only a few conditions that will throw any combination of codes at one time.
- After ascertaining what trouble codes appear with the P0446, the mechanic will typically inspect the EVAP system. This includes the purge valve, line, and canister.
- The mechanic will inspect the gas cap to make sure that it can handle pressure. If you are getting a warning that your gas cap is off, even when it’s on, replacing it will more than likely clear this code.
- The fuel tank pressure will be checked and monitored.
- After for the checks and fixes listed above, the mechanic will perform two tests:
- A smoke test, and they’ll use a scan tool to confirm that the EVAP solenoids and valves are operating properly.
Most Common P0446 Fixes
Here are the most common Mirai P0446 fixes:
- Gas cap replacement
- EVAP line replacement
- Replace charcoal canister
- Replace the fuel tank
Of all the items listed above, it would be wise to start with the gas cap and work your way to the fuel tank, since the gas cap is far and away the easiest and least expensive items to replace on here.
Here’s a great video on how to test your gas cap.
Good luck figuring out what is causing your Toyota Mirai to throw the P0446 code. We hope this helps. If there is anything that you feel like you could add, please feel free to leave a comment below. Have a great day.