Check your gas cap seal and make sure it is closed. If you drove for even a few miles with the gas cap loose you can get this code. Make sure it is sealed and drive, it could clear. Otherwise, replace gas cap and drive and see what happens. If it doesn't clear at this point, you have an evaporative recovery system leak in the fuel system elsewhere and may need a "smoke test" at a shop to find the leak.
po455 detects a large air leak in the evap system of your car. ck your gas cap 1st and make sure its ok, no cracks in o ring and that it is tight. after that you may neeed to seek a prof opinino because these can be tricky to repair