I just replaced both the vent valve and the purge valve on my truck. The vent valve is located at the back of the truck pretty handy to the spare tire. It is attatched to the side of the charcoal canister.. the valve assembly itself looks like a coffee cup. The list price at the dealer is around $200... but if you take it off and take it in and ask for one for a hummer h2 they are exactly the same part except the hummer one doesn't come with the pipe so you will have to reuse the old one. The one for the hummer h2 is about $45... if they don't have one for a hummer just take it in and they will have one there off another vehicle that will fit for about $50. The purge valve is on the drivers side engine compartment. If you take the rubber mud guard off the wheel well you can look in through and see it.. its right by a cord with plug on it that has tinfoil like wrapping.
Hay gays I'm getting the code p0446 vent valve problem. So i took the vent valve off and tested it with 12v power. And it seems to be working fine opens and closes. when i was doing this i was blowing in the hose to see if there would be any leaks when the valve was close there were no leaks. So could it be something else like the fuel tank pressure control?