The most common cause is the vent valve solenoid is stuck in the "closed" position.

This is the solenoid behind the gas tank (see diagrams) with the wires attached. Get only a factory brand Delco, nothing else.

I found this service bulletin that you need to follow in the same procedures as this Technical Service Bulletin (TSB) first before any other part changes are made. I know it's for pickups, but get parts for a 2005 Suburban.

TECHNICAL
Bulletin No.: 02-06-04-037D
Date: April 16, 2008

Subject: DTC P0446 (Restricted/Blocked EVAP Vent Path) Set, Check Engine Light On (Replace Evaporative Emission (EVAP) Vent Valve Solenoid Assembly and Add/Relocate Filter Box Using Service Kit)
Models:
1999-2007 Chevrolet Silverado (Classic) Models
1999-2007 GMC Sierra (Classic) Models
2007-2008 Chevrolet Silverado Models
2007-2008 GMC Sierra Models

Supersede:

This bulletin is being revised to add new style pickups to the models and update the correction information to include a new location for the filter box.

Please discard Corporate Bulletin Number 02-06-04-037C (Section 06 - Engine/Propulsion System).

Condition:

Some customers whose vehicles are operated in dusty type environments, such as farming or mining off-road type applications, may comment about the illumination of the check engine light, with a DTC of P0446 (Restricted/Blocked EVAP Vent Path) being set.

Cause:

Dirt and dust intrusion into the EVAP canister vent hose assembly, resulting in restricted air flow, may cause this condition.
Correction (1999-2007 Classic/Old Style Models)

After following the published SI diagnostics for P0446 and determining that the EVAP canister vent valve is the cause of the MIL light, replace the existing EVAP canister vent valve assembly with a new assembly. This new assembly is a sealed unit that is designed to be vented through a remote filter box.

 

I replaced the solenoid although I may have referred to it as a vent valve in my initial post.

Amazon part https://www.amazon.com/gp/product/B001KSCSQU/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1
vapor canister vent solenoid.

No change in my symptoms.

 

Visually inspect all gas tank / EVAP related tubes for the slightest kinks, dents or slightest compressions coming from or going to the gas tank. There is a remote possibility on gas vapor lines might have this condition if the gas tank was ever removed. There are additional valves on top of the tank itself that could be stuck shut.

Then if you can, when the gas tank is on vapors, carefully remove the gas tank filler neck and see if the anti splash back door is somewhat jamb shut at the base of the gas tank filler tube.

 

Update: Began pulling lines off the evap/charcoal canister yesterday. The first tube I pulled off, charcoal pellets fell out on to the ground. Thats the culprit and these pellets must be clogging my evap lines. New canister ordered, just need to figure out how to safely blow out the lines when it arrives. Any help?

 

Iv seen this issue many times. Usually occurs from over filling. When the pump shuts off don't pump in more fuel. Iv always removed the canister and just disconnected all the lines at the nearest solenoids to the canister and blown them out with shop air and install new canister. That's always worked for me.

You can also squeeze the lines off the canister and the ones that crunch need to be removed and blown threw

 

Thank you everyone for your replies. Spent today under the car pulling off the old evap canister and then proceeding to put compressed air through the lines to remove as much charcoal particles as I could. Got everything connect back together and went to fill up. Issue remains. Can get about 1.5 gallons in the tank before it shuts off. Frustrated and trying to figure out what to check next. There was a lot of charcoal in the lines leading to the vent canister, thought for sure clearing that would fix the problem.

 

There is probably charcoal remaining in one of the valves. If this problem has been occurring for some time it could have made it's way threw out the entire evap system.

 

I hope you pulled the lines off completely before blowing air threw them or charcoal is deffinitly inside every evap component.

 

3 lines came off the evap canister.

--1 line ran to the vent solenoid which i did not blow air through (its a short hose and when I shook it I didnt hear any rattle inside)
--a smaller line ran towards the front of the vehicle. once it passed the tank it had a connection I was able to undo. Therefore I was able to blow air towards the rear of the vehicle and ended up getting a lot of charcoal out this way. (yes the line was disconnected)
--a third line ran to the tank and I was unable to disconnect this line without dropping the tank. I loosened it from the canister and shook a lot of charcoal out and then decided to blow air into with the gas tank cap off (maybe a bad idea)

My next idea is to check a evap line someone on another forum said runs off the filler neck. I will also blow air through the small vent line from the canister to the solenoid valve. After that I am out of ideas.

 

Hello, don’t want to go through the whole post if not necessary if can even get a response. Is anyone still responding here?

 

That third line probably went into a vent valve on top of the fuel tank and is now plugged with charcoal. Might have to drop the tank and inspect it. Your deffinitly on the right track.

 

This exact problem started last week when I tried to fill my 2005 Z71 Suburban, and I thought it was the pump nozzle because I have had cutoffs before. Went to the same station but used a different pump today and had the same problem. In between the fill-ups I got a message to " tighten the gas cap" which I did. No DTC set. Does anyone know what causes this without setting a DTC and does this Bulletin apply to my problem ?

 

Update!
There was no Check Engine light so I had not checked for codes. Plugged in the scan tool and P0455 was stored which may eapxplain the message about the gas cap. I guess it could still be the Vent Valve, so will check it next..

 

The thread you want to read is "quick fix" for p0446. There are several causes for the 445 and 446 codes but I think this one covers about everything.

https://www.gmtruckclub.com/forum/t...m/forum/threads/quick-fix-for-code-p0446-evap-emissions-vent-circuit-low.18964/

Ted

 

Pulled the canister and it is full of loose pellets, so it needs replacing. The small line that has the blue retaining clip is stopped up with pellets. Do I blow into the canister end or the other end, and is the other end the on the purge solenoid on the engine?

 

The quick fix thread is long but you may need to try all the steps in that thread. Like Differently I think you've got a plugged hose. It could be any one of the three hoses. That thread in post #14 covers codes 0445 and 0446.

Ted

 

The vent solenoid you are concerned aboutis right there at the tank. Disconnect the hose and see if you can fuel the truck properly.
My was messed up for awhile. The new kit from GM was expensive, so I picked one up from the junkyard and put it on.
The new kit for my truck was gonna replace the solenoid and run the hose up to the top of the trans.

 

The quick fix thread is long but you may need to try all the steps in that thread. Like Differently I think you've got a plugged hose. It could be any one of the three hoses. That thread in post #14 covers codes 0445 and 0446.

Ted

After replacing the Vent Valve I opened the old one and it was not dirty, and I hooked up a battery to the the solenoid and it functions as it should. I do not have. SEL and no codes. Replaced the gas cap and still can't get gas in the tank. I do top off the tank when I fill it.. can that plug up the cannister? I am going to pull the lines off the cannister this morning and make sure they are open..

 

Yeah, the gas cap can set a code, but it won't keep you from filling the tank. After all, it's not even on the tank during a fill up.
The vent passage is blocked, somewhere.

 

Topping off the tank is verboten. Gas in an underground tank is way colder than ambient. After you top it off it will expand and travel through the evap system. You'll see the result when you open the canister and hoses there. You can possibly clear them by opening BOTH ENDS and using shop air. Sometimes they need replacing. Don't blow charcoal into your fuel tank.

Edit: You keep saying no codes. Didn't this start with a stored P0445?

Ted

 

The only code I initially had was P0455 and I with Tighten the gas Cap. I cleared it after tightening the cap and have not had any codes since. Took the canister off and it is shot, carbon is pouring out of the large pipe. The small hose with the blue lock is plugged with pellets. It must be the vacuum line from the Purge solenoid on the engine. Is it safe to to disconnect the line from the Purge solenoid and blow it toward the disconnected end that was attached to the cannister?

 

You don't want to blow charcoal pellets where they don't belong. Make sure each hose is disconnected at both ends before you blow it out. I've never had to do this. If it's not to much trouble then remove each hose completely one at a time and reattach so you don't mix them up. A new canister is filled with charcoal pellets but they aren't soaked with fuel.

Ted

 

Yes, disconnect at both ends of each hose before you try to blow them out.

 

Every once in a while I choose to read a post, such as this one, that has been resurrected. As I start to read, I get excited because @Motor City Rick is back, then I see the dates and am disappointed all over again!

 

I'm lost JackE. What'd I do?

 

For a while we had a user, screen name of Motor City Rick, he has some posts on the first page of this thread. The guy was amazing at knowing what the fix was. Especially if it involved wiring and needing wiring diagrams. He must have had every shop manual from the beginning of GM until now available! He just disappeared. We all miss his wisdom and guidance! He probably got tired of all of us " idiots asking childish questions" that @mommatried84 couldn't handle either!

 

I think he wore his two fingers out.

Ted

 

I'm all about playing around. 99.9 percent of the time I'm here for intertainment. But if I can help any the "weekend warriors" that's good too. As for the tight a$@ 's, "If they can't take the heat, stay out from under the hood."

 

Hope that fixes your issues