The speed
sensor is connected to the frame of the treadmill near the drive pulley on the front right roller.Take the plastic case off , only 4 small screws , There is a
small magnet or two on a plastic disk over the roller - pull this plastic piece over to the edge of roller on the side of the pulley wheel. The sensor tip must be close to this wheel to work - turn it on now and it should work right
steve staton, January 2013