P0446 Error Code Question

I have a 99 Tacoma with 3.4L V6. A while back the check engine light came on, so I invested in an OBDII tool to see what was up. It reported an error code of P0446. I ran this by a buddy who is a mechanic and he said to try replacing the gas cap. I did this and cleared the code and everything was fine for a few weeks, then it came back again yesterday with the same code. Has anyone run into this before or have any advice on what might be causing it? Thanks.

 

Thanks for the quick reply. Looks like it may be a little over my head. This what happens when you have a "buddy" who's a mechanic I guess...

 

p0446 code is an evaporation leak code, also p0440, p0441 and p0456, could be as simple as a loose gas cap, most common would be a charcoal canister. but you have a leak in the fuel tank region. If the gas cap was replaced and you used an aftermarket gas cap it may also be leaking as well due to a poor seal. Most likely though it is a charcoal canister.

 

Thanks again. I used an OEM gas cap and it's on nice and tight. I'll look into the charcoal canister. Sooner or later I just have to tear into it and scrape a knuckle or two. Where exactly is the charcoal canister located? I think the next thing I invest in will be a Chilton's manual.

 

Charcoal canister location: Online service manuals:

 

Awesome, thanks BeefTaco. Now I have something to do tomorrow!

 

Thread revival! (real question below)

This is the number one thread when I searched "Tacoma P0446" on google...wow...

Ok so on to the problem, since this thread is out there already no need to make another.

I have a '99 3.4L (5VZ FE) that throws the P0446 code on occasion. I'll clear it and won't come back on for a couple days to a week or longer (depending on the driving i'm doing). I see a faster return of the code with in-city stop and go driving, where as longer road trips won't kick the code on at all. There are no other codes that come on with this one at all. This has been ongoing for about 3 months now.

That being said, I replaced the gas cap and tested the VCV (it was within spec). What are my next steps that I should take to put this thing to bed?

 

Just piggy backing off of Tacotime- I'm having the same code and once in a blue moon it throws P0441. I realize it's most likely the charcoal canister, but am mostly wondering what the risk of ignoring it is. Truck runs just fine, the only quirk is I sometimes have a hard time filling the gas tank. The air doesn't escape fast enough as the fuel goes in, so the fuel backs up to the top quickly and kicks the pump off.

 

So mine came on again today after sitting at a stop light. It's been about 8 days since it last came on and most of my driving was highway over the weekend and before.

Can anyone lend some assistance or suggest solutions (taking into account my trouble shooting done already)?

 

My truck was throwing the Evap codes and I spent some time hunting down the issue, eventually had to use a home made smoke system on it but figured out that the fuel tank vent valve was the cause of the issue (as a result of this is where smoke was coming out of and should not have been)

This is a plastic valve assy that goes from the top of the tank over to the charcoal canister (how the vapors get to the canister). When I was getting parts the dealer told me that the seal will age and crack or the valve, again made of plastic, can break. I have highlighted in the attached with red arrow the part I had to replace.

After dropping the tank I found that there was a hairline crack in the plastic valve housing, which was creating the leak. While I had the tank out I replaced the seal and hoses associated with this valve. Total in parts will run ~100-150 depending on if you go dealer or online purchases, this included the hoses and seals which probably were fine, however if I am dropping the tank spending an extra 30 bucks to not have to do it again is worthwhile to me.

Just wanted to post what I had found and it has successfully fixed my truck. Likely would not have found this without smoking the system as could not see the crack in the valve until it was removed from the gas tank, but found the problem quickly and allowed for a one time effort to fix the issue.

 

Thread revival part 2. Realize this discussion is ancient but it's still #1 on google for 'tacoma p0446' so it might still help someone out there. In short my 2004 Taco 3.4 CEL came on @ 104k w/ a P0446 code (evap vent error). After checking for leaks unsuccessfully w/ propane and soapy water sprayed on hoses/connections, I decided to try cleaning my Mass Air Flow (MAF) sensor. Sensor head was definitely dirty - cleaned with carb cleaner, let dry, reinstalled. Took negative battery cable off battery for 10 min to reset the code. 100 miles later, no more code and the truck runs much smoother. Hope this helps. Thanks

 

I had this issue.. tried all the cheap and easy fixes but nothing worked so I'll give you 2 choices.
1. Park inside a garage and check for gas fumes overnight.
2. Smoke test your gas tank.
I had pinholes rusted thru top of tank around strap area. When your evap system attempts to pull a vac it cannot because of holes in gas tank giving same code as a loose gas cap. I also had NO wetness on bottom of tank to indicate fuel leak so at your age I would strongly suspect the tank?
Good Luck!

 

I have fixed a P0446 code on 3 separate tacomas.

You will never fix it without a smoke test.

 

Thread revival #3. Hahah.

I'm getting code P0440 and yes, this is still the #1 result on Google. I've replaced the cap, MAF, plugs, and checked a few hoses.

Next, I'm going to spray soapy water on the canister and see if I get bubbles. At this point I think my problem is the canister, a valve, or a crack somewhere near the canister (above the gas tank). This is on my fiance's 2002... Not my sigh 2011.

I'll report back after. I might end up taking it to a mechanic for a smoke test. Any cheaper ways to smoke test?

 

Is it "after" yet?

 

Yeah. We got it fixed @scoostraw I WISH this was only the MAF needing to be cleaned, that's too easy.

Our fix was replacing the Overfill (or overflow) canister if I remember correctly. They had to either drop the gas tank, or remove the truck bed (shop said lifting the bed was easier). Then they replaced a little overflow canister part and valve that's ON TOP of the gas tank. It was like $400, because I was too lazy and afraid to lower the gas tank myself.

This got rid of the smell of gas, improved gas mileage, and fixed the check engine light.

P.S. When you get gas and the pump automatically shuts off.... do NOT top off your gas tank a little more. All this does is overfill stuff. Shop guy said people that constantly top-off have this problem, and she always tops off her truck. Just a thought and a little extra advice for people.

 

Thanks for the followup xguntherc !

 

Happy to help.

Did you figure out ur problem? keep in mind that if you have the exact same code there's a big EVAP system leak and not a small EVAP system leak. So don't pay for the smoke machine. The shop already knows what's wrong, and will bullshit you into paying for extra.

When I say big I mean the big EVAP components. Not the small ones like a valve.