After seeing my CEL come on in my '05 Mazda 3 (just passed 100K mi.), I used my code reader to find out that the code was P0442. So I naturally came to this website to see what I could find on the subject matter. The only question on this site (at the time of posting) about this is questioning the validity of the CEL. I personally am going to believe the CEL/code is correct, because of the data that I have on my MPG (yes, I'm nerdy enough to have kept track of my MPG from the day I started driving this car). As you can see, my MPG has been plummeting for the last few months, and given how my current tank is progressing, I doubt it is going to go back up.
I also googled around and got pretty inconsistent answers being given from gas cap replacement (my current one looks fine to me), to the neck that the gas nozzle goes into (also looks fine to me), to plenty of other theories. Anyone have any idea as to whether this is something that is as simple as a new gas cap, or something that I can do on my own or if this needs to go into the shop ASAP? Is there anything else I need to check to make a better determination?