Originally Posted by mcnoople

Have you considered looking in the owners manual?

Clearly stated that when the light comes on it means your vehicle has fail a monitor for p0455 or p0456. If it is 455 (large leak) it can go away quickly. If it is 456 it may take weeks depending on your driving patterns. And yes it does actually require the car to be not running for the code to clear because honda now using something called "engine off natural vacuum" for it's evap leak detection.

As long as your honda says Check Fuel Cap it has not run the 2nd system test. If something is wrong with the car it will turn into a check engine light after running the 2nd test.