I think this is a common problem. Same thing is happening to my '11. Got customer service involved and still hasn't been fixed. 30K miles since mines been doing as you described. Ford keep my car for 5 days, drove it 35 miles and the light didn't come on for them. 2 days later it did and I called to try to take it in so they could run the codes since the light came on and they said no tech's available. Pretty frustrated myself.
It is happening frequently enough now I finally got it to the dealer while the lights were still on. Mechanic hooked up the computer and it showed nothing. We took a ride his computer hook up and it did it and still showed nothing!!! They are calling out someone from Ford and if and when they figure it out I will post in hopes it doesn't take you as long to find a solution as it did me.