there will either be a valve stem pressure sensor installed instead of the rubber valve stem, a band mounted sensor that is inside the tire and wrapped around the barrel of the wheel, or it uses the inputs from the wheel speed sensors to determin if one tire has more revolutions per mile(low tires roll more per mile than properly inflated tires.) if you have 2 different size tires front to rear that may be a cause, also the new pressure senor systems are very tempermental to temperature changes. nitrogen reacts best with the sensors to give correct readings in the cold.
i believe that all new fords use the band mounted sensor, which, to the tech would look like a factory wheel/tire combination but its missing the sensor from inside. the only way to find out if its there is to dismount the tire or break the bead of the tire and look inside of it.
who mounted and balanced you wheels and tires? (did they replace sensors) and what size tire combo is on right now?
the first thing i would do is check pressure and reset the tire pressure monitoring system