I just had that problem yesterday! I remembered my gas cap did not thread in right, and it must have set the code. I used some Vaseline on the cap and hole threads, after cleaning the dirt out of them first. Then I could tighten the cap properly. I might just get a new cap if it keeps being a pain. (If you Google search P0455, it shows that code is often caused by a loose cap.) The code did not reset itself when I fixed the cap, I had to use my (fairly cheap,at Advance Auto) Actron code scanner to reset the codes. So far, it is fine. The dealer could certainly reset the codes, it would come back if the cap is loose..