P0456 evap small leak detected

I was astonished when my beloved toy shouted at me “Close fuel tank cap!” from FIS message screen. Some time later “check engine” (CE) light lit on. My mechanic told me that small leak in tank vent system was detected and I should not bother until it pops up again. Such fancy environment-friendly system of gasoline fumes recycling is something that you can find only in USA models of VW group cars. Unfortunatelly my Audi A3 was imported from there and the CE light notified me again that something is not in order. Googling for small leak and reviewing gasoline subsystem in ETKA I realized how complex it is and how many possible failures we have. One hour research gave me 3 main suspects: faulty gas cap, erroneous purge valve or leaky carbon filter of gas vapors. Most people claimed gas cap replacemet did not help, so I asked my mechanic to take a look at purge valve first, right after he claimed hoses and clamps were in order. After repair, on my way back home, I really pissed off when I got “Close fuel tank cap!” again straight on my face. I stopped the car, stepped out, opened gas cap compartment and… found loosen gas cap! I called my mechanic but he said they did not manipulate around gas cap. In this very moment I was enlightened: I twisted on gas cap untill couple click sounds and it was still loose! Faulty gas cap, remember? Now the sequence of apperancse of intermittent faults was clear to me: they occured mostly after the night (sensor detected drop of evaporates pressure over night due to unsealed cap) and repeating intermittent failures are logged as permanent problem with CE. I was misled by statistics, I should start with gas cap replacement by the book, saving 25 euro for unecessary purge valve replacement. Anyway, my mechanic gave me gas cap for free, and it was really fair play, since it was his job to check all basic elements of failure. This way yet another adventure with car maintenance finished and I can enjoy back my 200 frisky DSG-geared mechanical horses, hooray!

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