Mastiff

I got both of these codes simultaneously, does that point in any particular direction? I previously had the "small leak", which turned out to be a crack at a connector on top of the tank, but I don't think I had the evap P0440 code that time. Haven't poked around yet, but pointers where to start would probably help.

jedg

I'd just spot for the smoke test if you can swing it. Around here that's around $100 for the test and they will mark the leaks for a person. Otherwise, you'll be chasing cats everywhere.

osvaldotp527

I fixed my P0456 code by replacing the evap canister Part #4861962AA. At first I tried replacing the gas cap. Replacing the gas cap didnt work for me but it has for some people.

EHarris

Three are a ton of posts on this topic. If you just want to throw $100 at it to see if it fixes the issue and 1 hour of your time just replace the system. Its the canister, integrity module and gasket. For an extra $20 you can do the Purge valve by the battery. One of those 4 will do it unless it's actually the gas cap and then its $10.

Rednroll

The purge valve is pretty simple to test. In normal operation the purge valve is closed, so if you pull off the purge valve and blow into in one end, you shouldn't feel any air coming out the other end.

Smoke test is likely the best place to start. I attempted to start there by purchasing a smoke tester, but never received it...and then resorted to throwing parts at it after confirming the purge valve seemed ok.
For me
1. New gas gap, no fix
2. Evaporator leak detection pump- Fixed

It's a kick in the nuts when the part which is intended to detect leaks in the system is the part that actually fails.