Mine happened to be the gas cap. Or so it seems. ::knocks on wood::
The CEL has been quiet for far too long now.....

All of the P0 codes test the same on every make, I have been dealing with this for years (at work). A smoke test is very useful but will only identify external leaks. It is possible that this code is caused by a leak past a valve internally, in which case it needs to be diagnosed by pressurizing the system and checking it incrementaly.

will replacing the gas cap turn off SERVICE ENGINE SOON LIGHT. mechanic says theres a small leak in gas cap?

you need a ODB2 code reader to read and clear the codes. The cap will fix the problem but the reader will clear the computer of the code.

P0452 Large Evap Leak
 

Hello, yes I’m replying to a decade old forum post, but I’ve gotten this large leak evap code on my dash as well. I have replaced my gas cap, and my purge valve. Was wondering if I would need to get my canister cleaned or get a new fuel pump. Any ideas are helpful!

Start with figuring out if you have a pressure test system or a vacuum test system It almost certainly is not a bad fuel pump or a canister issue.