Its a 2009 Prius with about 75K miles on it. I have scangauge on the dash as well as mini-VCI. It is setting PO456 code time after time. I reset it, but it comes back in about 50 mils of driving. Its not the gas cap, I turn it until it clicks every time. Something is wrong with evaporative emissions system, which I wouldn't care about, except it might mask some other fault code that is more serious, as it keeps check eng. light on all the time.
Try: 1) replacing the seal in the threaded edge of the gas cap; that is a wear item. 2) a new gas cap, or a gas cap for a friend's Prius that isn't throwing codes. 3) have you topped off? Maybe the fuel filler neck or other vales related to the tank/bladder are clogged or stuck in the wrong position, requiring replacement. EDIT: Bentley states, P0456 is same as DTC P0442 P0442 - Evaporative Emission control System Leak Detected (small leak). Trouble areas to resolve: fuel tank cap correctly installed fuel tank cap is cracked or damaged vaccum hose cracks are blocked, damaged, or disconnected in Figure 1 of the circuit description; reference the circuit diagram for the fuel system open or short in vapor pressure sensor circuit vapor pressure sensor open or short in VSV circuit for EVAP VSV for EVAP open or short in VSV circuit for CCV VSV for CCV open or short in VSV circuit for pressure switching valve VSV for pressure switching valve fuel tank is cracked or damaged charcoal canister is cracked or damaged fuel tank over fill check valve is cracked or damaged ECM Let us know what the solution was.
+1 try a different gas cap 1st. can't assume the cap is good. or emissions stations can check your cap with their tester (if your state has emissions testing).
Extended warranties are typically a waste of money for most consumers. These insurance companies are in the business of making money for themselves. Their underwriters know the odds/longevity/probability of the covered components failing. A few people here/there may win the lotto and have a big ticket item covered, but the vast majority of the time, these companies make MONEY! Besides, these warranty policies have a lot of exclusions/loop-holes. Found the fuel/EVAP system training guide; its intense. Hopefully a known working gas cap will solve the problem.
