Ok, I'm lost... I have an 07 H2 with a new canister and gas cap that throws an error "tighten gas cap" within the 1st mile or 3 min only from a cold start. Throughout the rest of the day it's never mentioned again Help!

 

did you replace the purge solenoid as well? check the filler neck at the gas cap for rust as well, maybe it is not sealing properly. you can try clean it up with some sand paper or steel wool or scotch pad.
but it can also be pinholes in the filer neck tube or pinholes on your fuel pump.
also make sure whatever hoses you disconnected are fully seated when the parts where changed

 

Thank you. I'll check into it and let you know.

 

I may have missed it in chain- what is the exact code number you are getting? If you don’t have a cheap scan tool - Amazon has them cheap.

 

You missed it by 5 years! 10/4/25 threads:

 

"Tighten Fuel Cap" Rabbit Hole - Hummer Forums - Enthusiast Forum for Hummer Owners

 

9/10 times is the vent solenoid on top of the gas tank. Happens from overfilling/fuel splashing up and sticking it open. Or if your charcoal canister failed and sent debris up to it. Could also be purge solenoid but less likely.
NEVER top off the tank. Once the nozzle clicks off, you're done. Otherwise fuel gets into places it shouldnt.