Engine Light/Gas flapper gone!!

[Linghoney]

I have a 2004 Pontiac Vibe 136000 miles and since the beginning of summer my check engine light started coming on. Not sure of the specific code that the computer pulls, but its an emission error that leads everyone to believe that my gas cap is loose. Long story short, gas cap is always tight, rubber gasket seal good, very minimal corrosion to the opening of the tank. However, my fiance thought that maybe there should have been a small spring loaded flap at the entrance of the neck that was now missing...??? I often smell gas fumes after making a turn in the car when the tank is on the fuller side. Is there a flap missing? Is this a big problem? And its it going to effect gas milage in any way?

Thanx in advance, Heather Lee

[zyzyix]

How bad is the corrosion? Have you checked the filler pipe (leads from tank to the gas cap opening) for corrosion as well?

[Linghoney]

Surface rust only and no corrosion in the neck. I'll try and post pic.