I'm going through this again right now. I had P0446, P0442, and P0441 simultaneously. I just fixed P0441 by testing and replacing the purge VSV (vacuum switching valve) which is the VSV under the hood and closest to the MAF sensor. Toyota nomenclature also calls this the "VSV for Evap".

One of the causes of P0446 is the VSV which is at the charcoal canister (at the rear underside of the car). Some years ago I resolved the P0446 by preplacing that VSV. You can probably test it while it's still attached to the canister, but I find it easier to test it by removing it. Currently I have the P0446 again (along with P0442), and In my case a new VSV isn't solving the problem, so I have to do further testing.

I have a DIY on this forum showing how to test the VSV at the charcoal canister (Toyota nomenclature also calls it the "VSV for vapor pressure sensor"). Here is the link to the DIY which has instructions and information: Testing VSV For Vapor Pressure Sensor . It includes a video I made, but the video is a bit lame, and my arm is blocking the view, but it gives you the idea along with the clear instructions/photo you can read in the DIY.

There's another VSV below the purge VSV. Toyota nomenclature calls it the "Close Canister Valve". It is normally open, so air should flow through it until it is activated, then air should not flow through. I need to test that one on my car.

 

Do you have issues filling up your gas tank? The vent solenoid is going to vent the fumes from the fuel that would saturate the charcoal canister. If the hard line is rusted, that is one source of the problem. As it’s not supposed to vent to atmosphere.

Will need to use a smoke machine to locate the leak. In the event the hard line is broken, use nicop hard line. This is less prone to rust.

 

Thanks John for your help.

75 Aces, no problem with filling the gas tank.

 

Rubber hose or hard line leaking. Failed vsv.

 

Hello, what is your scan tool.?

 

I've got an INNOVA 3100 abs scan tool

 

For the P0446 code, you might want to check the EVAP vent valve and the charcoal canister. These are common culprits for this issue. You can also inspect the hoses for any cracks or leaks. If you have access to a smoke machine, that can help pinpoint any leaks in the system.

 

No smoke machine but I'll check what I can and hope for the best.
Thanks for all suggestions!

 

Just so we're all clear, there are three evap VSVs on the 2004 Corolla. The VSV very near the MAF sensor is what the aftermarket calls the "purge" solenoid. Toyota calls it the "VSV for Evap". The VSV right below it is the "Close Canister Valve". The VSV on the charcoal canister is the "VSV for Vapor Pressure Sensor".

Really, Toyota uses different names when you look at the official parts listing and the official Toyota FSM (Factory Service Manual). I wish they'd get everything organized with the nomenclature, but it is what it is.

 

Thanks John...that helps!