I have a 2002 Elantra and over the past year, I've taken it to the dealer 4 times for the check engine light being on. Every time, it's the code p0455 (evap leak) and they say that my gas cap is loose. I know how to tighten a gas cap (3 clicks...), but they told me I should tighten it to 7-8 clicks which I did. The second time, same thing, but they replaced the purge valve. Third time, same thing, but they replaced the gas cap. Now, it's in the shop for the 4th time and my warranty is up on 9/1. They tightened the gas cap and said the problem is fixed. I do not consider this a resolution. Something is causing my gas cap to become loose.

Has anyone else had this problem or know how to fix it? Also, why am I not seeing the code p0457 which indicates a loose fuel cap?

Thank you very much for your help!

 

Maybe the filler neck that the cap tightens to is warped or bent.
They are made of soft aluminum or plastic in most cases.