Cel p045

Driving along in my 08 Optima yesterday and the CEL came on. Ran it by Advance, and it showed P045. I had filled up earlier in the week, but the light didn't come on until yesterday. The gauge was just under a half a tank when the light came on. It was already tight, but removed the gas cap, re-tightened it, and have driven about 50 miles since then, and the CEL is still on.

Any ideas, does the CEL light reset after a while?

Not sure on your mileage but you should still be under factory warranty. It is either the pressure sensor located on top of the fuel pump assembly or there is a blockage in the EVAP system.