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What are fault codes p0441 and p0446 and how do I fix them? Has any body else seen these?
 

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I had the CEL just this week on the way to work! Pulled the OBDII meter I bought last year that evening when I got home. It read the P0441 code. Did a few searches on Tundrasolutions and the Net and they said look for a loose hose and that's exactly what it was:) It was right on top of engine, popped it back in, cleared code and off I went:)
 

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This just happened to me a few days ago. i have a 2005 DC Limited and i have found that if its not the rubber parts of the hose in the engine compartment, or a loose gas cap, it could be a switch or solenoid on the CHARCOAL CANISTER. A new canister is about $500. Thats IF the switch is built in the canister. i personally dont know if it is, and i havent had time to take a look.
doees anyone know more info on the canister or had this problem?
 

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2015 Toyota Tundra DC SR5 5.7L
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This just happened to me a few days ago. i have a 2005 DC Limited and i have found that if its not the rubber parts of the hose in the engine compartment, or a loose gas cap, it could be a switch or solenoid on the CHARCOAL CANISTER. A new canister is about $500. Thats IF the switch is built in the canister. i personally dont know if it is, and i havent had time to take a look.
doees anyone know more info on the canister or had this problem?
They are external to the canister and replaceable.
 

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My 2001 4.7L Tundra had P0441 + P0446 codes. In my case the fix was trivial. There is a hose that runs from the charcoal canister on the right of the engine compartment to the engine. The hose was not clamped and had come off the plastic nipple - in 13 yrs the rubber has lost some of it's elasticity. Pushed it back on with a clamp. Given the age of the truck the evap hoses will need replacing at some point but with a clamp all is well for now. Took 10 mins to diagnose and fix...
 

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I have a 2000 Tundra and I am getting the p0441 code only. In addition, when the vehicle has been running a few minutes it starts to idle rough. Hoses all look in decent condition and gas cap is tight.
 

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I just spent a bit of time diagnosing my P0441 and P0446 codes on my 02 Sequoia. I made some mistakes and thought maybe others could learn from them.

I started by replacing the old cracked evap hoses in the engine compartment which were all connected but original and in bad shape. This didn't fix my problem but was a good thing to do. Without doing any research about the evap system design and how the codes are set, I took a guess based on the code description (P0441 vent control circuit) and bought a vent vsv solenoid thinking this was the solenoid on the canister (it isn't). When I got the solenoid, i tried to install it on the canister and discovered it wasn't the same solenoid. Thinking I had made a mistake on year model selection, I zip-tied it to the existing solenoid bracket and connected the hoses and hacked the plug keys to get it to connect into the system. Turns out what I had actually ordered was the vent solenoid located in the engine compartment and this solenoid is normally open where the canister bypass solenoid located on the canister is normally closed so this was never going to fix my problem.

So next I borrowed my neighbor's techstream laptop which has a very useful utility that performs the exact evap test process that is executed during normal vehicle operation and allows you to monitor the vapor pressure sensor during the various steps of the test. Based on the test steps and vapor pressures observed, it should be possible to determine if there's a leak in the system or non-functional solenoid. The test process is a little complicated but there are lots of youtube videos with detailed descriptions of the exact test steps.

Toyota has changed the evap system design over time and the one in use in my 02 Sequoia is called the intrusive design and it uses 3 solenoids. There are a purge and vent solenoid in the engine compartment and a solenoid called the canister bypass valve (located on the canister) that connects/disconnects the canister to the tank where the pressure sensor is located. While running the techstream test utility, I could confirm my system was able to build and hold vacuum pressure so I didn't have a leak in the hoses or purge and vent solenoids which is good. But the automated test opens/closes the canister bypass solenoid and looks for rate of change of the pressure in such a way that diagnosing a bad canister bypass valve is tricky. The techstream utility also allows you to activate each solenoid independently to confirm operation. So I actuated each of them one at a time and would blow through them to see if they were opening and closing as expected. It turns out the canister bypass valve was stuck open and could not close.

So now I needed to source the correct solenoid as I didn't want to buy the whole canister. New canisters are >$250. Decent looking used canisters from low-ish mileage sequoias are only about $125 on ebay so this was an option but I didn't really want to spend that much on an 18 year old canister. Searching for canister bypass valve turned up nothing for the Sequoia as I guess Toyota doesn't sell it by itself. But I took a picture of my canister bypass valve and can see Aisin stamped on it. So I googled Aisin vacuum switching valve and found it is a VST-024 available for about $30. Installed it and the evap test passed within a few minutes of startup. Got rid of the cel that's been driving me crazy for weeks.
152745


So the point of the long post was to try and help others learn from my experience:
1. Don't guess at the problem and throw parts at it hoping to fix these codes. There are too many different things that can cause problems in the evap system and chances are you'll replace good parts like I did.
2. Having access to techstream made troubleshooting the system much easier than doing it by hand. Yes, you can actuate all the solenoids using a 12V supply or power probe but techstream makes it even easier so you don't have to mess with clip leads while trying to hold the solenoids and blow through them. Techstream also pulses the solenoids like the ecu does so you don't overheat the coils. Techstream is pretty cheap but seems like you need to have a 32 bit windows machine so that's something to consider.
3. Study how your specific evap system test works. The systems change over the years and the names of the parts change. There are many youtube videos with good classroom-like descriptions of the designs and specific operation steps. If you understand how your system works and can logically test it, you won't waste time chasing things you don't need to.

I did all the wrong things while debugging this and it took me forever and made me crazy. Don't be like me.
 

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2002 Sequoia SR5 4WD
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@jbarnett2501 thanks for sharing your experience, I am just starting to chase a P0446 code now and this helps a lot.

Is this the solenoid that goes on the canister by the spare tire? If so, the Toyota part is 90910-12264 or
Denso 184600-3981
 

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yes that's the solenoid on the canister. all the exploded parts diagrams i found for the evap system didn't list that part separately, only as part of the canister assy. rockauto didn't have anything listed for bypass solenoid, only purge and vent. how'd you find that? guess i could have asked at my dealership but i hate going there. watch some of the youtube videos that explain the whole evap process and they'll tell you where the P0446 gets set. i don't remember any more. good luck.
 
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