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Anybody with dreaded P0446 on a Toyota? #2745707 09/16/12 06:02 PM
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Vikas Offline OP
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I have posted this on ToyotaNation Camry area too.

I have 1999 4cyl LE. I have read all of the threads on this particular topic but still do not know what to do now. I started getting P0446 since last month and the code comes back immediately after resetting it. My mechanic says he sees a lot of them on Camry and Corolla and replacing the rear VSV solenoid fixes it. He had a genuine Toyota part in stock but after he removed mine, realized that mine had three hoses and the one he had was the one with the two hoses variant. So we got the correct one from NAPA.

Well, the code came back in couple of trips.

Is it possible that could it be a bad NAPA part? I can ask him to get the genuine Toyota part but if that does not fix it, then my leverage on him will be reduced greatly. He will do whatever I ask him but then I have to be better diagnostician than he is. Right now he has thrown a part at it based upon his previous experience. Having read this forum, I sort of knew going in that I would have to be really lucky if only VSV was going to fix it but I decided to take a chance.

I have put my EOBD scanner on the car. The Mode $06 data shows all of the six test being completed successfully. Unfortunately, I do not have the decoding ring for Toyota 1999 Mode $06 to interpret them. On the I/M, everything except EVAP MON is incomplete and the CEL must be going off when that test is being attempted to run. My mechanic's fancy scanner is down and he won't get it for at least another week or so. Mine is adequate but does not have factory support or two way testing.

Given the specificity of the code i.e. circuit fault, I did not even bother to get a new gas cap as I am thinking it would have no chance of causing this particular error code but then I do not know what the Toyota engineers were thinking when they wrote their ECM code. At this stage I am desperate. Should I just throw a brand new OEM cap at it? It surely can use a new cap after 13 years of faithful service but is there even a remote chance that would fix the P0446 code?

I have got lots of tools such as electronic copy of factory service manual, generic scanner, mightyvac vacuum pump with gauge, dmm etc but the limitation is I do NOT work under the car unless it is on the lift.

How would ScannerDanner or ScottyKilmer or EricTheCarGuy would approach this one i.e. real diagnosis vs parts replacement? I would rather not follow any algorithm which is of type
1) Replace part A
2) Did it fix the problem?
Yes - Done
No - go to 3
3) Replace part B
..

Some of the factory service procedures are like that. I know some of you have lot of experience on this specific problem and I hope they consider this one as an internet challenge!


Update:-

I just bench tested the older VSV. It works fine. It holds the vacuum on one port and the other is flow through. There are no leakage. Vacuum is released when the voltage is applied. It passes all the test listed in the service manual.

This means there was no need to replace that VSV and something else is the cause of the P0446

Re: Anybody with dreaded P0446 on a Toyota? [Re: Vikas] #2745708 09/16/12 06:03 PM
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Vikas Offline OP
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oops, it should have been posted to the mechanical forum. I would appreciate if a forum moderator can move it there.

Re: Anybody with dreaded P0446 on a Toyota? [Re: Vikas] #2745724 09/16/12 06:11 PM
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What is p0446?


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Re: Anybody with dreaded P0446 on a Toyota? [Re: Scott_Tucker] #2745729 09/16/12 06:15 PM
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hypervish Offline
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Originally Posted By: Scott_Tucker
What is p0446?


EVAP Emission Control System Vent Control Circuit


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Re: Anybody with dreaded P0446 on a Toyota? [Re: Vikas] #2745732 09/16/12 06:24 PM
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expat Offline
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We had it on our Matrix, it happened after driving A very steep, bumpy road with a very full tank of gas.
I cleared the code but it came back a few days later.
We lived with it for 2-3 months , before it mysteriously went away and never (touch wood) came back.

Re: Anybody with dreaded P0446 on a Toyota? [Re: Vikas] #2745742 09/16/12 06:41 PM
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98Corolla Offline
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I currently have the same problem with my 98 corolla, p0440 (I think) and p0446, both emissions related. I just live with it and reset the codes every once in a while to make sure nothing else is wrong.

I purchased this vehicle from my dad last nov and didn't investigate it until this spring, I found out, I was just a few months out of (Toyota's recall warranty) this spring (believe it or not) because my corolla was under 150,000 miles.

If you have that low of mileage you might want to investigate it.

Best of Luck!

Mark

Re: Anybody with dreaded P0446 on a Toyota? [Re: Vikas] #2745786 09/16/12 07:25 PM
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Boomer Offline
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You won't pass inspection in PA or many other states with that code showing up.


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2017 VW Golf All Track 1.8 liter gas engine DI, 25,500 miles Castrol Professional VW 505 5W-40
Re: Anybody with dreaded P0446 on a Toyota? [Re: Vikas] #2745833 09/16/12 08:02 PM
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Vikas Offline OP
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I have only the P0446 code.

It has 185K miles, so it is NOT eligible for the Toyota warranty. I also looked at the NAPA box and it is stamped "Made In Japan". Given that the old part tests out good and the new part is most likely made by the OEM manufacturer, I see no need to ask my mechanic to swap with the genuine Toyota part. I don't want to fire my "one bullet" on that approach!

There is a TSB EG004-99 which tells to replace vacuum control valve assembly but my VIN is outside the range of the RSB. So my car should have had the updated part. But I suppose even the updated part can go bad in 13 years! Unfortunately there are no diagnostic procedures listed on how to verify bad assembly. This part will cost me about $50 mail order.

From my research, many of the people suffering from this code find relief with the new VSV but I am not so lucky.

The nuclear option is the canister but that costs close to $400!

Last edited by Vikas; 09/16/12 08:04 PM.
Re: Anybody with dreaded P0446 on a Toyota? [Re: Vikas] #2746148 09/17/12 07:39 AM
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Vikas Offline OP
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I was told on ToyotaNation that LeakySeals is an expert on this one. Paging LeakySeals please!!

Re: Anybody with dreaded P0446 on a Toyota? [Re: Vikas] #2746264 09/17/12 09:57 AM
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HerrStig Offline
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There are a number of parts in that system including the canister, the rear VSV and a pressure sensor which looks for vacuum when the evap test is conducted. The canister can get a crack, the hoses can split , the rear valve can clog, or the sensor can send incorrect information. On the Camry the canister, sensor, and rear vsv are all under the rear of the car. There is a slight chance of a pinhole in the tank filler tube as well. The rear VSV routes the vapor stored in the canister to the engine when the car is started, the front vsv applies engine vacuum to the tank assembly just for the test. If the tank assembly won't hold vacuum, it won't hold the vapor pressure either, thus the code is triggered. I would suspect that iof the leak is large enough, the test will show NO vacuum being applied and THAT might trigger the 446, though the front vsv is working properly. I fixed a 446 on my Toyota with a new front VSY, though testing the old one as well as I could didn't seem to show anything wrong. The coil resistance was proper, and the valve seemed not to leak.
Don't rule out a dirty electrical conection on the under the car parts.. vsv and sensor giving ...an improper reading. The system is complicated enough that they must have hired a BMW engineer to design it.

Re: Anybody with dreaded P0446 on a Toyota? [Re: Vikas] #2746508 09/17/12 01:41 PM
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What bothers me is that the code says circuit fault but the laundry list of the causes have everything including gas cap leak.

I have glanced at the front i.e. air cleaner assembly where the stored gas vapors are burned in the engine but I have not looked at it thoroughly. There was a youtube reference where the front hose got pinched under the air-cleaner housing and the computer was throwing the same P0446 code on similar vintage Camry. Another youtube reference shows a completely clogged air vent off the canister. But that Toyota had a real problem of not being able to fill the gas i.e. pump used to shut off all the time.

There should be only one hose going all the way back from the rear canister to the front EVAP control solenoid in the engine, right? I need to check if that can hold the vacuum. I need to check if the front EVAP control solenoid is electrically working and opens and closes correctly. I need to feel the other rats nest around canister area to see if any of the hoses are split or disintegrating. As I said before, they look good from 3 feet distance.

That canister will set me back $275 in parts alone :-( At least the time is on my side and I have until July to get this fixed or find a work-around.

So please, have more ideas coming my way.

- Vikas

Re: Anybody with dreaded P0446 on a Toyota? [Re: Vikas] #2749969 09/20/12 10:28 PM
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I feel your pain. I've been battling a repetitive P0455 (large) leak on my gas tank evap system. After utilizing a small vac pump, I discovered a leaking vac valve up front.It would hold fine in a static condition, but when pulsed about once per 1/2 sec. it would fail to hold. That was the key to diagnosing the fault. I replaced it, the CEL went off for months and all was well. . . for awhile.

Now it's back. Instead of throwing parts at it, have your mechanic do a smoke test of the gas tank, evap system, and engine.


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Re: Anybody with dreaded P0446 on a Toyota? [Re: Vikas] #2756980 09/28/12 09:22 AM
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It is said that the canister can fail and dump charcoal into the lines clogging things up. A brand new VSV can fail this way.
I'd do a close inspection of everything under the car. We have had trouble with spider nests in the air vent line making it hard to put gas in.

Re: Anybody with dreaded P0446 on a Toyota? [Re: Vikas] #2757150 09/28/12 12:53 PM
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Miller88 Offline
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Circuit failure? That's an electronic thing.

Check that all of the wiring and harnesses/connectors for the EVAP are in tact.

A rusty wire could be cuasing this, a worn out or corroded connector too ...

When I unplugged a coil while trying to diagnose a misfire on a Hyundai, it had coil circuit failure.


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Re: Anybody with dreaded P0446 on a Toyota? [Re: Vikas] #3013112 05/25/13 01:09 PM
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KB1 Offline
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FIXED the P0446 Code!!! Been on almost 2 years but smog time came around. I got a junk yard canister off a newer 2001 camry. Thought it would fit my 99, nope, different size hoses and VSV. Started to try to figure out [censored] was wrong with mine. The VSV was good but the large valve mounted to the canister with the fresh air hose attached would leak a small amount in one direction when it was supposed to be sealed. Swapped the one off the junkyard canister onto mine and Boom fixed. Passed smog too! Dealer wanted to install a new canister which is really the only option for them since the individual pieces of the canister are not for sale. Had to post this to add to the long list of problems with Toyotas and the p0466. I would post a picture of the valve thing if I knew how. Oh yeah Do Not waste your time with an aftermarket (Dorman) VSV. I had one to try to rule it out and it failed in one drive so I put the stock back on.

Last edited by KB1; 05/25/13 01:12 PM.
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