here's most of the codes you'll see. there are more but these are the most common.
P0449 Evaporative Emission Control System Vent Valve/Solenoid Circuit
make sure the air line and connector are connected, it most likely means you need to replace the evap solenoid.
sometimes just weird shit happens when you fill up your tank, drive with the gas cap a little loose or off. just clear the code. if it comes back look into repairing or replacing that solenoid.
if you don't have a scan tool, disconnect the positive cable for 60 seconds and it should be cleared. you'll have to reset your clock etc. but it does the job.