I have a 2005 F250 Crew Cab FX4 with the factory park assist system with the sensors in the bumper. About 6 months ago I was backing up and noticed the system was not beeping. I looked down and sure enough, the switch on the dash was "on" or "disabled." The next day I turned the ignition on, engine not running, put the truck in "reverse" and checked for the clicking noise from the sensors. All sensors were fine except for the inner driver side sensor. I bought a new sensor, plugged it in, and no change. I checked for voltage, ground, continuity, short to ground, and anything imaginable, but still nothing. I bought a new module, swapped them out, and still nothing. I took both the new and used sensors to another "working" sensors plug and they both worked. I am running out of options except for taking it to the dealership and pay the money for the computer hook up. The only thing I get when I put the vehicle in reverse is one beep from the speaker and then the system "disables" itself. Any thoughts?