P1448 - EVAP Purge Solenoid Valve, located on the Charcoal Canister near the gas tank, is not closing. The Charcoal canister is located under the bed, near the gas tank. You should be able to test it by unplugging the connector as shown above, and connecting the two pins to a standard 12 volt car battery with test alligator clips. If you do not hear it click when power is applied, it is most likely bad. You can try blowing it out with an air compressor and some WD-40, but it should probably be replaced. Part # 911502 is pretty cheap.
P0455 - Because the vent valve is open, the evap pressure sensor sees no pressure. If you are only getting this code, it might be the gas cap. If you are getting both this code and P1448, the P0455 code will most likely go away after P1448 is resolved.
The complete list of items used in this project, and other projects, can be found in the Parts List below.