You have to be careful but start the truck and put it in reverse. While someone keeps the truck still place your finger over the sensor, actually touching it. You can feel a slight snap in your finger. The one that does not snap is the bad sensor. I confirmed it with a Ford test computer.
The system defaults to "Off" if it senses a problem with a system component, including the sensors, wiring, and little speaker in the rear trim panel... 95% of the time it's a single, failed bumper sensor.
A good Scan Tool, SPX, Snap On, will be able to access the reverse sensor module and run a self test. If if is a sensor it will tell you which one it is. Had the same issue with my 01 and I used a SPX Genisys. It told me exactly which one of my sensors was bad. Replaced it and all good now.

waaalaaaahhhhhh!!!!!! Your insight was right on. I did your test with my wife behind the wheel and 1 sensor had no response. Just for giggles I swapped that sensor with another one just to see if it was in the connector. It was not. The problem followed the sensor. Thank you so very much for your help. Without guys like you in these forums alot of people would be up !@#$ creek without a paddle. Be safe and keep it on four wheels
Good to hear you figured it out and should be pretty simple to fix.
Also good that your wife didn't seize the opportunity to run your ass over.![]()