So I was at my local DMV paying my tags and when I'm done and driving off the car says check gas cap. Somebody had stolen it in the parking lot. Seriously who does that? My question is how do I get rid of the message from the dash. Yes I already replaced the gas cap with a new one from the Honda dealership.

 

Easiest way would probably be disconnect the battery and then connect it again.

 

The message should clear itself after you drive around a spell with the new gas cap securely attached. You don't need to do anything special to reset it.

 

That is correct, drive it around until the car computer realizes it is indeed fixed.

Sometimes, turning the car off, waiting a bit, then turning the ignition on, let it be on for about a minute, then turn motor on, can speed it up a bit.

Your car goes through a series of "checks" each time the ignition is first turned on. it looks for sensors not reporting at all, does a quick calibration of the O2 sensor if its already warm, and will use the MAP sensor (manifold pressure) to get a barometric reading.

It does these things anyways if you immediately turn the motor on, but it is good to wait a few seconds at a minimum

EDIT this is why things like oil pressure, ABS, SRS, etc.. flash at first. most lights go out after a few seconds, some will stay lit until engine is turned on