FOD is any object(s) that does not belong on piece of electronic hardware, drive motor, or elevation motor. If dust, dirt, or water make it on to an electronic's board surface short circuiting, speed sensor contamination, and excessive mechanical wear and tear is the result.
Let me explain. Take a look at the photo on the left for example, and look closely at the amount of dirt on the surface of the board, if the right circumstances are in place the dirt can act as a conductor between two pins on an integrated circuit.. If this happens that chip can fail and bring down the whole board.. If that doesn't happen, the dirt can "blanket" critical components causing excessive heat, which in turn can cause premature failure.
Speed Sensors in treadmills work on a primitive optics system for feedback to the MCB Controller, if you have a hairball between the optical face and the mechanism it's sensing, your whole treadmill is not going to work.
Lastly, hair, pet fir and accumulated dirt work its way on to the screw drive of an incline motor causing it to work harder on the larger inclines.. This same dirt penetrates Drive motor bearings and wreaks havoc with the sealed ball bearings
We all know lubricating your belt and deck is the number one way to extend a treadmill's life, but this is the one that is most commonly overlooked... Which is funny, because it takes little time and it's free.
A FOD-prevention strategy is simple, with the power off to the machine, unscrew the motor hood and vacuum out all the dust and dirt, be thorough because you only need to do it once or twice a year.