tire pressure sensor fault warning light on

If the pressures are correct the most common failure would be the sensor inside the tire itself. They have a battery in them and normally they last 7-9 years before they are low enough to cause problems. You need a TPMS scan tool that will activate the sensor and with it you can also see what the battery status is on the other tires as well to determine if you need to replace those as well. Most tire shops or places that do tire repairs will at least have the tool. Ford uses two styles of sensor some are banded in place in the drop center of the wheel while others are the ones mounted to the valve stems. They run between 20 and 50 dollars each depending on which ones you use. If you know how to break down a tire you can buy the sensor and install it but you would need to know which it is first.