Shaddow

I have a 2k2 SE and today when I started my car my SES light came on. At lunch I ran by Autozone and had the read the trouble code and it came back as P0455 "The PCM has determined that a large leak exists in the evaporative emission control system"

Is this the "gas cap is loose" code I always have read about here and never paid much attention to?

I looked as much as I could manage through posts but since the search is down I decided to ask.

Should I do anything more or will it shut itself off after some time of the gas cap being screwed on right?
Thanks!