I bought my 04 used and had that problem immediately off the lot. At first the dealer service writer blamed it on the salesman who gassed it up before delivery with the engine running. He reset the computer the light went away...for 12 hours. It happened again. I still had warranty left so they replaced the cap. But I believe the computer has to be reset after it happens. By the way, my cap looked good, but the seal was defective. Also, if you take the cap off with the engine running, you will get the same message, and I believe it has to be reset. Not sure how to reset the computer since mine was under warranty and handled by the dealer service dept.