For the last week it has been extremely cold where I live (varies between -27 to -33 degrees Celcius). Is it possible for a fuel cap check valve to freeze open?
Last night leaving work the display on my 2012 Honda Civic told me tighten fuel cap and within 10 minutes of driving the warning corrected itself. This afternoon drove into work with no problems until I entered the parking lot at work then the display said "check emission system". I know it is not the seal of the fuel cap because it is brand new OEM from Honda.
Update: I turns out that is exactly what the problem was: A frozen check valve. Thawing the fuel cap for an hour and a half indoors and re-tightening the cap then driving a 100 km to reeducate the computer followed by a 5 hour shutdown to allow the system to do internal pressure checks. Result: Problem solved the emission system is now functioning normally.