I corrected the P0455 code on my 04 Cav by replacing the "Canister Purge Solenoid". (located on rear right side by gas tank. You'll see a hose running from the 'cannister' to the solenoid.)
(Part number PV155 from AutoZone) I think Napa has them also.
I have seen other reports that have found the 2 wire harness that connects to this Solenoid to be bad , but mine was fine, so I replaced the Solenoid itself, and the code has not returned.
