Evaporative Emissions Vacuum Switching Valve

You'll be replacing the evap VSV valve vacuum switching valve someone will be along shortly to show you in the diagram exactly where it is generally hoses slip on it and plugs into something and pretty uneventful sometimes the hose can be split not completely plugged up things like that to get the same code this switches between your evap canister and your vent valve at the tank or something like that so you're not letting off unburned hydrocarbons into the atmosphere there routed into a charcoal canister where when the car is driving the vacuum switching valve can open and suck those vapors from the canister and burn them completely it's basically the gist of all that mine goes out in my van all the time 01 sienna.

 

I can believe P0446 is the code, but wherever you found "Replace Evaporative Emissions (EVAP) Vacuum Switching Valve (VSV)" as the fortune cookie for the code is a place you shouldn't go back to when looking up codes.

The key is to remember that trouble codes are never telling you what you need to do to solve a problem. The computer that logs the code isn't smart enough to know what you need to do. It can only tell you something it noticed, and the job of figuring out what to do about it is up to the human.

The actual fortune cookie for P0446, looked up in the repair manual, is "Evaporative Emission Control System Vent Control Circuit". You'll notice that's just naming something, not giving you marching orders to replace something. A fortune cookie that sounds like marching orders is just bogus.

Also, when you look up the code in the repair manual, the next thing you see on the page is the "Detection Condition". That's the real thing you need, because it tells you what the ECM actually noticed to make it set that code.

For this code, the detection condition tells you that one of these two things happened:

• No change in fuel tank pressure when purge VSV and pressure switching valve are opened
• No change in fuel tank pressure when fuel tank is depressurized until 740 mmHg and purge VSV is closed

and the ECM noticed this on two separate trips.

So what's happening is the ECM is commanding these valves to open or close, but the expected effect on the tank pressure isn't happening. That can be a problem with the valve itself, but can also be with wiring to the valve, or leaky tank or vacuum hoses, etc.

There are 14 pages of troubleshooting steps in the repair manual for that code. Those steps are how you can work out what the actual problem is that set that code, and once you know that, then you can plan how to fix it.

 

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Here is the workup for P0446 : https://attachments.priuschat.com/attachment-files/2018/04/143457_cip0441.pdf

You might find this thread helpful : P0446, Techstream TBP Fail, and CCV Replacement | PriusChat

Have you already checked the low hanging fruit, like the gas cap (2 clicks) and associated o-ring? (some have used spit or silicon as lube)

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