I have a 2011 RDX AWD/Tech package with 20,000 miles on it. A few weeks ago I started the car and the "tighten fuel cap warning" came on. So I popped the door and the cap clicked so I removed it and put it back on. I drove home (46 miles) The light stayed on, when I started the car the next day the light changed to "check emission system" and the little check engine light came on. So I called the dealer and they looked at it and said "you left the cap off at some point." But they found some loophole and didn't charge me the $119 dollars for diagnostic. A week after the dealer visit I was again 90 miles away from home and the light came on again "tighten gas cap" this time I am 100% positive I tightened it. So I re-tightened it anyways and drove home. The next day I started the car the light was gone and as I drove somewhere the "Check emissions system" light came on again. It's in the shop right now and they have no idea and are calling the "techline."
Both times the light came on it was several days after I had filled the tank the first time I was at about 70% and the next time 40%