p0446 and p0450 solution checklist?

I'm working through the p0446 and p0450 error codes on my 2000 Tacoma and I figured if I find the solution it would be nice to post what it was somewhere on the internet.

Thus far - I've completed the following tasks and cleared engine codes after each change:

1) Replace gas cap: No change - same error codes p0446 and p0450

2) Replaced the Vapor Pressure Sensor: No Change - p0446 and p0450 remain

3) replaced the Charcoal Canister: p0446 pending and two tests need to be completed. Basically I still need to complete EVAP test #5 of the drive cycle, which is warm up the truck for 10min at idle - drive 45mph immediately for 5 minutes - then slow down to 25mph for 15min and perform at least two stops of 30 seconds in length. Don't turn off the engine while performing the test.

4) Test the VSV valve with a 9v battery and listen for a click: Done. Valve clicks and if I blow into it with my mouth it holds pressure and releases pressure upon applying power.

5) Test the other VSV attached to the charcoal canister: This is currently the one I'm unsure how to test. I attach a 9v battery and hear a faint clicking, but nothing as solid and loud as test #4 VSV valve. I'm also not sure which side to blow into as I don't seem to get the same effect as #4 when I blow into the valve. The fact that the valve does make the clicking noise makes me think it's *probably ok, but if I'm going to replace any part next I may as well do this one.


Currently I have a p0446 pending and two more tests incomplete. I just recently installed the charcoal canister, but I have a suspicion that the error codes are not going to go away. This will leave me stumped and forced to take the truck to the mechanic. I would think the only other thing would be a failed ECM. They say for the p0446 that it could be a hose or crack in the gas tank, but if I'm getting a p0450 error code, then the only other part that could be failing is the ECM I believe.

If anyone is able to verify my above testing procedures and clue me into any other EVAP parts I might be missing in my troubleshooting I would be thankful. I'll also make sure to post what ultimately fixed the issue, which seems to be missing from nearly every post on the internet. Most posts just have questions and not a follow up on the solution. Clearing your engine code after replacing the gas cap is useless, because it just leaves your OBD-II codes as "incomplete". You're just masking the problem and not solving it.

 

Welcome to the Forum.............

Let's see if we can help with some information. You P0446 code is : Evaporative emission control system, vent control circuit malfunction.
You are looking in the right area and you are replacing a lot of parts. It does help rule out the problem, but it is expensive. Since this is a Circuit problem, you would deduce that the problem is electrical in nature. You have two VSV valves that can be checked with a simple ohm meter, set to measure reisistance or ohms. Measure both of them and I would bet your second VSV valve that is giving you mixed signals, is the bad one.
You are doing a fine detective job trying to run down this problem. Good Luck.

You may want to include a little background info, such as what year and what engine size is your problem.

 

Following up: After a couple months I'm back at it. check engine light finally came back on after my tests completed. I'm off to purchase the VSV solenoids as they're the last part I haven't replaced

My engine details:
3rz-fe Tacoma engine model 2.7 liter 4cyl

VSV part numbers:
90910-12130 vacuum switch valve

25860-75160 VSV VAPOR PURGE VACUUM SWITCH VALVE

 

Did you figure this out? I have a po441 code and when i add power to the vsv vapor purge vacume switch nothing happens