Fuel tank pressure sensor?

That car doesn't use an FTP. It instead uses a natural vacuum leak detection module. That is part of one of the lines that connects to the charcoal canister from the tank. There is a known failure point on them, the filter assembly cracks and you get leak codes because of it, there is a TSB about those -
TSB 10-24-10
DTC P0455 / P0456 DUE TO NVLD FILTER CRACK - VEHICLES BUILT ON OR BEFORE 7/19/2010
DATE: 12/8/2010
ISSUE: Some 2011 Fiesta vehicles built on or before 7/19/2010 may exhibit a check engine light with diagnostic trouble code (DTC) P0455 and/or P0456 due to a crack in the Natural Vacuum Leak Detection (NVLD) Module filter.
There are 2 possible part numbers depending on if you have the 4 door or the 5 door Fiesta.
4 door is - AE8Z-9J279-E While the 5 door (hatchback) is AE8Z-9J279-F

In your case it is not the cracked part but that the NVLD either failed or the wiring to it has been damaged. Both of those codes pretty much mean the same thing, the NVLD cannot communicate with the powertrain control module, the 451 is "NVLD signal range/performance" while the U code is lack of communication from the module. So basically the PCM tries to get the data from the NVLD but it cannot talk to it which means there is a performance problem with the sensor which sets both codes.
I would start by unplugging the sensor while watching the sensors output on a scan tool, see if the numbers change. If they do the wiring may not be the issue. However to verify that I would use a simple test light to check for power by connecting it between the Blue w/red (battery) and Brown w/yellow (ground). The light should come on as the power is full time hot. If it does and you can watch the live data then keep the test light connected to ground and touch the other probe to the Green w/orange wire. If the data changes when you touch it the circuit to the PCM is good and the module is bad.

Which module is good? The NVLD or? How did you test it?