Interesting, I have this same code on my Flex. All positions BUT floor are working, the door position motor has been replaced as it was stuck on defrost originally, motor has been replaced twice actually as the first replacement was made of Chinesium and made one hell of a racket after a while, the second is a Motorcraft one, It will cycle through all positions, briefly touch the floor and settle on Defrost. The Floor Defrost mix is the only one where a tiny bit of air flows on the floor, the Vents and defrost work fine.

My question is, since the motor is functioning, the door is obviously moving, could something be physically broken in the ducting that is allowing the door to go all around instead of actually stopping? If it allows the motor to run past its position sensor, that could cause an open to ground.

It's not an issue until it gets cold out and our feet freeze, summer is fine since the vents work. Trying to get a game plan down before I tear into it a third time. The damned motor is up behind the instrument panel and is not at all easy to get to.