Evap canister question

[BJ Bryan]

I have a 2007 Tahoe with 175k miles and the dreaded P0455 error code and difficulty refueling as the gas pump keeps turning itself off.

Tonight I took apart the hoses, blew them out with air, and put things back together. Drove for about 10 miles and no error code...but then it came back on. My question is this:

1. How do I know if its the square EVAP cannister or the circular shaped solenoid with the charcoal filter?

2. Are aftermarket parts okay for this type of application? I've always bought ACDelco parts from the dealer...but the dealer parts are literally $300 more than aftermarket. I dont mind paying it if its the right thing to do, just curious on some opinions here.

 

[Geotrash]

I have a 2007 Tahoe with 175k miles and the dreaded P0455 error code and difficulty refueling as the gas pump keeps turning itself off.

Tonight I took apart the hoses, blew them out with air, and put things back together. Drove for about 10 miles and no error code...but then it came back on. My question is this:

1. How do I know if its the square EVAP cannister or the circular shaped solenoid with the charcoal filter?

2. Are aftermarket parts okay for this type of application? I've always bought ACDelco parts from the dealer...but the dealer parts are literally $300 more than aftermarket. I dont mind paying it if it’s the right thing to do, just curious on some opinions here.

The problem is in the pellets being released from the canister, so it’s the square canister that needs to be replaced. Unfortunately, you will probably need to blow out the lines again. And if it’s reached the solenoid, you may need to remove that and clean it out as well.

Buy the OEM canister from rock auto. Their prices are better than anywhere else, and I just bought one from them a few months ago.

 

[Fless]

When you blew out the lines, did you get any charcoal bits out? If not, and you can blow (mouth) air through the canister, it's likely not the problem.

It's easiest to test the canister vent valve off the truck by removing it, then trying to blow (again, by mouth) through it when it's not powered. This valve is normally open, meaning if 12v isn't applied to the terminals, it should pass air through. When 12v is applied to the terminals -- polarity doesn't matter -- it should be sealed and no air should pass through. They can be intermittent, so be sure to test with some on and off action.

One thing to be sure is that the truck ignition is off when filling; otherwise the evap vent valve could be commanded closed. A blow-through test with ignition on and off can also confirm the proper venting and command.

Check the evap vent valve filter, too. It may be on the valve or a few feet remote, depending on the mfr. Lots of times they're plugged with dirt and should be replaced. Some of the valves come with a relocation kit to move the valve and filter up higher to avoid it getting clogged too easily.

Note, too, that the evap test is done only under certain conditions: fuel tank 1/8-7/8 full, cold start, etc. It won't run after a warm start.

EDIT: If you end up getting the canister then I'd go with a GM part. For the evap vent valve you could go with a good aftermarket brand, but we've found GM OE or ACDelco (if OE isn't available) to be the most reliable.

 

[BJ Bryan]

Hey guys, I replaced the canister but the issue hasnt totally been fixed. The check engine light has gone away (for now at least) and I was able to pump about 10 gallons in today before it clicked off. Now I'm back to having the gas pump click off every 5-10 seconds. I replaced the vent valve about a year ago with an OEM part...should I replace it again or what could be going on here?

For what its worth, when I removed the canister, I could hear dirt shaking around and a few ounces of gas leaked out.

 

[Fless]

What you heard in the canister was likely charcoal pellets, not dirt. Be sure your lines are clear (like in the first post where you said you blew them out). Also, no liquid gas should be in the canister; that's an indication that the fuel tank was overfilled at one time or another. Stop pumping gas at the first click off, when it's filling normally.

Ignition off when fueling. This removes power from the vent valve and it should open.

Blow out the line from the canister to the canister vent valve. With ignition off or the vent valve electrical connector removed, you should be able to easily blow air through the valve. If it's difficult, the valve may be stuck (partially) closed or the filter clogged. A quick test and inspection should tell you if it's what's causing the fueling issue.

 

[BJ Bryan]

Hey guys, was out again this morning and I can easily blow through the hose from the cannister to the vent valve. I also unplugged the electrical connector and tried to fill it up...still no luck. Is it possible the vent valve has failed or do I have a problem somewhere else?

One other thing, I verified 12 volts to the connector...it's always 12v btw... regardless of if they key is in the ignition or not.

 

[BJ Bryan]

Any ideas? I've checked everything again and still getting the error code and the pump stops every 5 seconds when I fill it up with gas

 

[Fless]

The vent valve 12v supply should be off when the ignition is off; I don't think it matters if the key is in or out of the ignition. The valve should be open with no voltage applied. You can verify circuit function with a test light of an appropriate load. Can you blow air through the valve with it disconnected from the supply voltage, as stated in post #5?

 

[BJ Bryan]

The vent valve 12v supply should be off when the ignition is off; I don't think it matters if the key is in or out of the ignition. The valve should be open with no voltage applied. You can verify circuit function with a test light of an appropriate load. Can you blow air through the valve with it disconnected from the supply voltage, as stated in post #5?

Yep I can blow through it regardless of ignition status, it is constantly showing 12 volts as well. Could it be an electrical issue?

 

[BJ Bryan]

Also, I've taken all the other lines apart as well, including the line to the gas tank and everything is wide open