What is the fix for this code other than a new gas cap which I've already tried. The new cap was brand new Honda OEM from dealer, twist the cap plenty, so it's not that because the code keeps coming on.

Had my mechanic check for leaks and he found nothing??

I really do NOT want to take it to the dealer. Has anyone experienced this same problem, and if so, what am I looking to change and how much will it cost me?