2004 GMC Sierra

I was hoping I would never come across this problem again, okay listen to me, have you replaced your fuel cap yet? The reason I ask is because the O-ring starts to crack and does not seal the fuel tank, if you have filled up your vehicle without shutting it off it will also set this code, but the most important question is if you do not let your vehicle get below a half tank (which is smart) and then you let it get below a half a tank, especialy on a hot day, the E-vap valve fails to open and allow the fumes from the fuel tank to escape it will also set a code, the only way to fix this is with a scanner and manually open the valve several times until it gets unstuck. Sorry, if I can be of any more assistance let me know you can contact me on yahoo anytime.