Originally Posted by 101gargoyles

Took that info out to mine that was showing only a P0456 code and equipped with the stock locking gas cap. Noticed filler neck surface that mates to the cap O-ring was sort of nicked/scratched a bit and had some type of oily film/dirt on it. So went back out with some Scotch Brite pad and cleaned that all up. Then I removed the cap O-ring and rolled it over to use the opposite face. Used a Q-Tip to lightly apply the Vaseline and closed her up. No I didn't try to clear the code manually I just figured if it's cured the CEL will disappear after enough run cycles. NOT Well after a few weeks I took her in to my mechanic for an oil change and asked him to check out system for any other source of the code. He only found a different code that was the one for a bad rear oxygen sensor-I think he said P1*** something. Replaced sensor and now no codes at all. Wondering now if the cap work I did fixed the original code and just by coincidence that second code popped up in the month or so from the time I got the original code to when I finally got around to doing the cap cleanup.