Large Evap Leak Code Help

[CromulentWord]

2006 Aveo
Runs Great.

I've been getting a check engine light consistently that reads out code P0455. I've replaced the gas cap twice and changed out the vent valve but it just comes right back on about a day after resetting the OBD.

What else should I be looking at? Is this a known issue with this year? I've had a couple mechanics take a look and no one can find a leak... I'm pretty stumped.

[petrified.rabbit]

the way the edu checks it is verifying there is a "vacuum" on the system to see if there it sealed. it could be a bad charcoal canister, or something along the line of a leak. I have also seen o rings in the fuel pump dry rot enough to allow a leak.

[TechGeddon]

I had the same issue, it was the gas cap. I see you said you replaced it.

Have you tried clearing it, and completely sealing off where the cap goes with a piece of foam or heavy rubber?
Access to some of the tank is directly under the back seat (should just pop off while pulling up on it (its on metal clips, you wont break it)

Check sensor lines, or any leaks as mentioned from rabbit.