check engine light for EVAP

hello all,
i have just joined this forum as a last ditch effort for the check engine light. It was on when i bought the truck 6 months ago for the charcoal canister. Before spending the money, i replaced the EVAP system sensors under the hood and on the canister. Light came back on. New gas cap and fuel neck. Light came back on. Finally bought a new canister....gosh darn light came back on. its throwing a 440 and 442 code. the tank doesnt seem to have the vacuum when i take the cap off. Any suggestions for this?

 

I have same issue with my 04
Anyone have suggestions?

 

I've been dealing with this same EVAP issue for 2 years now on my 2004 Tacoma. I've replaced the cap, sealed a few hoses and smoke tested more times than I can count. The light keeps coming back with no discernible pattern or reason. It also comes with a comforting sporadic gas odor near the tank. My mechanic and I are stumped. I believe it is unfixable at this point.

 

Put a smoke machine on it. There is a vent out of your charcoal canister that you'll have to plug. Look for the smoke. No one here owns a smoke machine though.....

 

OP I would be suspicious of the fuel check overfill valve gasket, seen these go bad and nobody catch on to it till you've replaced everything else
Part # 77177-33010
Goes on top of the gas tank so you'll have to remove/lower the tank

 

I had leak codes until I replaced the charcoal cannister and pump/sensors. No more codes. When I looked at the old system I think the tiny vacuum pump had jammed.

Things to note. There is no vacuum on the system when you open the cap because it's basically open to atmosphere all the time through a highly hidden vent under the gas cap connector lip. The system wakes up ~ five hours after engine shut off and runs a series of vacuum tests. It takes two tries (two days) to set the CEL codes so if it's OK at the shop it's not necessarily so. The easiest way to get to it is to undo the six box bolts and raise the box a few inches. You can do that without disconnecting the filler system or back lights.

Thanks to ODB2 regulations it's a stupidly complex system made to check an unnecessary complex system on the truck.

 

A further thought, your problem could be the result of overfilling the tank. The refuelling valve on the cannister has an internal diaphragm that could be ruptured if you overfill. You'll then end up with a leak to atmosphere through the filler vent. Has anyone had any experience here?

 

Today I had a look at the charcoal cannister I took out. Sucked on the hose to the refuelling valve and sure enough the diaphragm is ruptured! Vacuum pump can't draw a vacuum and you get CEL codes.

 

I too am having the same issue, after replacing cannister, both solenoids, fuel filler assembly, the gas odor and EVAP codes po440/442 still come on when the gas tank fuel indicator falls below 1/2. Im reading in the posts above that the gasket for the fuel valve on tank can go bad? How about the fuel check overfill valve itself? Anyone having any success with this being the culprit?

 

First, the bolded text is incorrect. The fuel tank is not open to atmosphere all the time. If it were, the system would never be able to maintain any kind of vacuum. You are correct that it takes normally two failures to set a code, however some vehicles will set a code on first failure if there is a large leak detected. (P0446 I believe is the code)

As for why so many people have problems with the P0440, P0442, and P0446 codes is because they are truly difficult codes. Sticking solenoids and erratic pumps can cause these codes to pass then fail then pass then fail.... you get the picture. The only way to really be sure of finding the problem is to run multiple smoke tests. Unfortunately my shop is in Alabama, so I can't help you there...lol. If you can smell fuel, then you have a leak. Sometimes these leaks can be small pinholes in the filler neck. I have seen more than one filler neck drive a tech crazy. There is a common failure of the VSV valves as well. I suggest taking it to a place that can smoke test it. Guessing at parts can get VERY expensive.

 

What attention to detail! Yes the cannister vent valve is closed during the vacuum test cycle but otherwise the fuel tank is open to atmosphere.

 

I've also replaced my fuel filler assmbly, gas cap, valves/seloniods and canister after we did two smoke tests and noticed no visiable leaks. I would hope that the issue would not be related to these parts again? So, I'm now focus and down to the gas tank area. How about the gas tank fuel cut off valve/fuel pump gaskets deterioriating causing the fuel leak and odor? You menation erratic pump? I assume the fuel pump? I've also read on other forums where gaskets/rust can be the the source of the problem?

i appreciate your feedback and time.

thank you!

 

I posted several times speculating about what it might be. My later posts are about the refuelling valve which I'm now sure was my problem.

Do you or pump jockeys overfill your tank? Don't. Also, the rubber bellows on the fuel fillers (if you're in a state that has them) might cause enough internal tank pressure to rupture the refuelling valve bellows. One way to tell might be if you have frequent shut-off's when you're filling the tank. The bellows opens a valve that allows more tank venting when you fill it.

 

I am sorry, but I disagree. Both the vent and purge valves are closed with engine off. The entire purpose of the EVAP system is to PREVENT off-gassing of the fuel system. If it were open to atmosphere, then it would not be serving it's purpose. I have been certified in, and diagnosing EVAP systems for over a decade. Your information is incorrect.

 

BamaToy you need to read the emissions part of this very good article. I would recommend it to everyone else as well.

http://www.tacomaworld.com/forum/technical-chat/123729-1gr-fe-pdf.html

 

Why thank you for helping me support exactly what I have been saying. This taken DIRECTLY from the PDF file in that post...

 

Congratulations, you've read the first sentence now read the rest of the article.

 

OK, I am done with you and your attempt at showing you know these systems better than I do. This will go nowhere. Not only have I read the entire article, but as I mentioned, I have worked on, diagnosed, and trained others in these systems for years. The fuel vapors in the EVAP system is NOT vented to the atmosphere. Period. If it were, it would violate federal mandate laws on emissions. If you feel you are so right, why not do some research on more than just a single PDF file.

It is simple, the purpose of the EVAP system is to PREVENT fuel vapors from venting into the atmosphere. What part of that sentence do you not understand?

 

New canister assy, fuel filter, gas cap, new plugs, rear o2 sensor, all new hoses...
I resealed the fuel pump gasket... What are the other 2 units on the tank?
Still getting 0441

 

Runs like crap for 2 minutes after filling tank