I was getting the P0455 code and replaced the solenoid/canister in the rear quarter panel and no more check engine light.

Part # for the solenoid is 25932568

 

had the check engine light come on in my 2005 monte carlo ls. (50,00 miles) went online to search for answers and began throwing parts at it. replaced pcv valve--no help. replaced purge solenoid under hood--no help. finally took it to the dealer and problem was the vent solenoid. it is located on drivers side in the rear up behind the gas filler hole. it looks like a campbells soup can with a hose and electric connection. cost under 40 bucks for part. only 10 minutes to replace---slide off pole and swap electric and hose hookups. cured my check engine light code po455 for $156.00 at dealership. this was the next part i was going to replace. cost an extra 116 dollars at the dealer cause i got frustrated!