Ok, replaced my EVAP Canister vent control valve and erased the code. It came back. So for my P0455 it was neither the gas cap, nor the EVAP canister vent control valve. (once i solve this issue, i'll reinstall both OEM parts. The aftermarket get cap sucks)
I dug into the FSM, and they list the causes for the various codes.
P0488 is the DTC for the vent control valve. I checked the OEM part i removed and it functioned fine. No different than the Dorman part i replaced it with. I kinda regret not testing the original beforehand. I applied 12V to the connector and it clicked shut per the FSM troubleshooting methods (page 435 and on) and when i resistance checked the coil, i got around 16ohms on both. Didn't check the wiring harness yet to make sure I had 12V on it. SO my conclusion is that unless you have P0488, there is no need to change the evap vent control valve.
Checking the FSM for P0455 shows a different solution other than bad gas cap, or the EVAP vent control valve.
P0455 refers to the "Evap Canister Purge Volume control solenoid" that is located under the hood. Page 422 in the FSM above.
Cause is listed as this
EVAP canister purge volume
control solenoid valve circuit
An excessively high voltage signal is sent
to ECM through the valve
Harness or connectors
(The solenoid valve circuit is shorted.)
EVAP canister purge volume control
Ive yet to start troubleshooting this one yet. Giving it a another shot of erasing my P0455 code and seeing if it come back. But not holding my breath since it came back once.
This valve is located on the intake manifold bolted to the rear passenger side. Gotta pull the plastic cover off.. One side goes to throttle body and the other the rear EVAP system.
Rockauto.com has the part....it's $91. Standard Motor Products #CP743 It's $91. Gonna troubleshoot before replacing