P0446 - Evap Control System Vent Control Circuit Malfunction

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Check Engine light came and the code is: P0446 "EVAP Control System Vent Control Circuit Malfunction"

I am planning to replace Vacuum Switching Valve on my 1999 Corolla. My Rolla has 150K

I am looking for any suggestion, video OR instruction to replace Vacuum Switching Valve on my 1999 Corolla.

Given link below for part, please suggest, which is the right part:

Thank you.

There should be a number of videos that you can find on this online - P0446 and other EVAP related codes are common on many 8th gen Corollas - mine included.

I also have a diagnostic check list and some scans of the factory service manual concerning the EVAP system on my photobucket site in my signature.

As for the parts - hard to tell without them next to the actual vapor canister - there are a number of vacuum hoses, electrical connections, VSV, CCV, and cutoff/vent valves that could lead to a P0446 DTC being set.

Absolute best way to chase these issues down is to get the EVAP system "smoke" tested. Many times, these EVAP issues come from faulty valves, poor electrical connections, or cracks in the hoses, housings, and fittings. A smoke test will zero right in any leaks.

FWIW - my P044x codes were related to a bad plastic cutoff valve on the top of the gas tank. $30 part - but would have cost over $600 because of the labor involved to drop the tank. Dealership tech was able to print out a copy of a blown up diagram of the EVAP system and part number for the cutoff valve - I was able to do it myself in 1/2 day.

Fishexpo101. Thanks for quick response.

Can you give me the location of 'Vacuum Switching Valve', This is located under hood or near gas tank.

I couldn't find links posted by you, can you please send me the link also.

Thank you,

Both. Usually, it is the one that under the car, as its location allows that valve to be more easily subjected to environmental damage.

Try this - top level link to my photobucket account,

You should can also find similar information on the Autozone website. Just look under the "repair help" link on the homepage, drill down to "vehicle repair guides" and follow the links. Might have to register to look at the content.

Another option is to invest in a (hardcopy) Haynes repair manual. Generally run about $25 or so - if you want to do any DIY work on the car, this generally will pay for itself the first time you use it. Alldata has an electronic subscription program that allows you to get the same sort of information as well as the latest TSBs. Both are great resources.

It took little longer to update the forum but still I have P0446 code on car. I have changed EVAP canister, two hose and checked every thing near gas tank. At this point, I am assuming nothing wrong near gas tank.

I guessing now that some problem under hood. Can some one guide me to look under hood and resolve the issue. Any picture under hood or video for 1999 corolla will help.

Just for you guy weeks before CEL came, I did replace valve cover gasket because of burning engine oil

You made sure to clear the ECM, drove normally, and the P0446 popped back up?

Possible you bumped one of the vacuum lines under the hood when you replaced the valvecover gasket. That could lead to a P0446 DTC popping up. Look around the throttlebody and airbox to make sure all those hoses are connected to a fitting, none of the hoses have excessive cracking or other physical damage. Any exposed "nipples" on the airbox or TB is a sure sign that a vacuum hose fell off. Don't remember any of those lines being "capped" from OEM - meaning that all of those fittings should run to a hose.

Also possible that there are issues with the valves on the gas tank itself. That was the case with my P0446 - ended up being the cut-off valve on the very top of the gas tank. Only way I could get to it was by dropping the tank.

If you haven't already got the EVAP system smoked checked - now would be a good time to do so. Those will quickly pinpoint leaks in the EVAP system - let you know exactly which valves are not functioning correctly, any hoses that are leaking or missing, if there are multiple leaks in the system. Well wroth the diagnostic charge IMO - that is what found my damaged cut-off valve, when they ran the smoke test, they were able to zero in on the valve within minutes.

HI Fishexpo,

Yes, I have cleared CEL and drove normally couple days, almost 80-100 miles and P0446 popped back.

I will double check throttlebody and airbox area to make sure all hoses are correct. Might it's time to do smoke test.