Of course, I start my car to go to the service appointment and the light is now off!
Lost count but it seems as if it took at least 10 trips to make it turn off but it did eventually go off by itself.

 

I have a similar story -- 8 months ago my 4 month old Camry had showed "check engine" after I didn't tighten the gas cap enough. Took it to the dealer and they instructed me about the need to really tighten that cap; they also reset the "check engine" light. Since then I've been pretty careful to tighten that cap . . . but the "check engine" light showed up again two days ago. I checked and tightened the cap but several starts later I still got the error. Took it in to the dealer and they showed "P1423 Fuel Tank Gross Leak, Needs Fuel Filler Neck." The dealer replaced this under warranty and the "check engine" light is again dark. Apparently it's enough of a problem that Toyota is paying for the repair ($350+) without question.

 

I found P1423 code listed with many other codes under the header, Auxiliary Emission Controls.