It's not the first time I've filled it up and pulled away without putting the fuel cap back on, and probably not the last, but I just did it again. Like every other time, the check engine light never comes on and no DTC is ever stored. I'm just thankful for passing motorists letting me know I've left my zipper down or I discover it myself sometime later.

I'm not trying to prove a negative here but shouldn't I have had some type of EVAP system DTC flagged because of this non-fault error? Can something else be malfunctioning that should, but doesn't, recognize the error and wouldn't have its own DTC if it was faulty?

I would think you would eventually get a Service Engine Soon light with the p0455 gross evap leak code, it might take at least25 or 30 miles of driving though.

That makes good sense. I never get that far before I realize the cap was left off.

The system doesn't even check for that until the vehicle is parked. EONV (Engine Off Natural Vacuum) only occurs if a certain amount of tank temperature drop has occurred since shutoff and only if the fuel level is between 1/4 and 3/4. That's why the ECM has self-control of the ECM Relay, so it can wake itself up to monitor the tank independent from the state of the ignition. That's also why vehicles can sometimes go for days with the cap off and no MIL, then suddenly the light pops on. Since EONV only happens after an unspecifiable time period with the ignition off, folks almost always get the MIL after a workday or first thing in the morning.

PS - If you have an evap leak and want to cheat the MIL for any reason, one way to do it is to be a "tank topper" and never let the gauge fall to 3/4 or less. The EONV will never happen and the MIL will never light.