I've Changed everything and the error code won't go away!!!
 

I have a P0455 Large EVAP code that just will NOT go away....here is what I have done so far...

I have a 07 GL450 and I needed a CAT. I changed the cat and O2 sensors on the pax side and shortly there after I got the gas cap error.
I purchased a gas cap from Amazon and cleared the P0455 code.
I eventually failed my emissions test due to a bad gas cap so I went to the dealer and paid a gazillion dollars for an OEM gas cap.
I passed my emission test so I thought everything was good.
Shortly there after I got the check engine light again. Scanned it and it was P0455 AGAIN!
I changed the purge valve as that was less expensive then the Charcoal canister
about a week later the check engine light came on yet again
I changed the charcoal canister and the tech said the one he took out has fluid which he suspects was gas in it.
after the new charcoal canister has been put in the light came on AGAIN!
I keep getting the gas cap error in the dash.

I would appreciate any insight because I've changed everything I know to change pertaining to this error
I don't know what else to do!

Do you have emissions testing where you live?

yes and ironically I just passed

why do you ask?

why do you ask? (Sorry for the duplicate)

Take a careful look at all of the hoses that connect to that system. It's likely just a small crack or tear in a hose. Worst comes to worst a shop should be able to smoke test it to see where the leak is.

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Then, pragmatically, why worry about it?

cause I'm gonna have to pass again next year and if I have changed all of the components that have to do with that system I dont wanna be screwed next year.

Did you change the valve that is in the engine bay? Or the one in the rear fender well?

both

the one in the engine is the purge valve
the one in the pad side wheel well is the charcoal canister

In the wheel well, there is a valve and the charcoal canister. You said you changed the canister (full of fuel); did you also change the valve? That valve is often the culprit in the 0455 error.

so I got the smoke test and sure enough it was the vent valve...I called back up the shop where I got the charcoal canister changed and they said they changed it but the shop that did the smoke test said it is old. once they get it on and retest it hopefully I will be good to go.

I just want to post that you hit the nail on the head. the changed the vent valve and all seems to be well so far. I still have to drive until the EVAP cycle completes but from their smoke test its good.