I have a 2006 Honda Accord. Since my purchase three years ago, the instrument panel states, “check gas cap” three separate times. Each time I took it to a Honda Dealership and they run a series of tests (smoke test and gas cap test) and the results have been negative. My warranty has expired. Just last week the “check gas cap” came back on again.
It says “gas cap” but the sensors don’t really know what is causing the large gas tank pressure, or vacuum, leak. It may be the gas cap; or, something else.
This problem may still be covered by warranty because you took it to the dealer while it was under warranty and it wasn’t resolved. Check your warranty.
give a wipe to the filler neck and gas cap gasket next time you get gas, worked for me. It might take 50 to 75 miles for the code to clear. One weird one under warrenty was the pump that pressurizes the system for the test failed.
Check one of these addresses to find out your rights under the lemon law, that may mean that problem is still covered under the warranty until they can get it right.