Try disconnecting you're battery

 

yeah then give it a drive cycle after that...if the light stays off you're golden. if it pops back on you can try swapping the cap again, but it may be the filler neck side of things.

 

Check fuel cap,,is a assumption the computer throws out there in the programm,,sometimes its right,,but whats happened is that you have a leak of some sort in the evaporative system,,probably a gross leak,,if the cap light come on,,If the cap doesnt fix it ,,check what the other guy said about the hoses going to the tank,,also you should smell fuel usually if its a big leak,,look under the hood and underneath and see if you can pinpoint a fuel smell,,or notice any vacuum lines knock off,,Worst case senerio,,you can have a vent solenoid not closing and the pcm does the evap test it fails,,but that would require some testing