Hey guys, my son drove my civic for about 80 miles with no oil filler cap. Now I am getting a P2646 code. I just changed the oil and replaced the oil filler cap. Can anyone give me some input on what the p2646 code is, how to address it and could it be from driving with no filler cap?

Just a little more info:
Car has 145k miles on it
Oil last changed 4k miles
STP oil filter used
5/20 oil used.

Many thanks.