A code p0455 most likely means one or more of the following has happened: A loose or improperly affixed gas cap
A non-conforming gas cap (i.E. Not factory/original brand)
Other leak or damaged piece in EVAP system
Possible Solutions With a p0455, the most common repair is to: Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
Otherwise, replace the gas cap, and/or
Inspect the EVAP system for cuts/holes in tubes/hoses (you may hear a vacuum noise or smell fuel), repair if necessary