on the back of the bearing housing is a ring with slots/holes in it, the sensor detects pulses as the hub turns,this tells the ABS if the wheel is rotating or stationary.strip the hub off and check the ring is not covered in rust particals the back plates go crusty also that the ring has not become detached from the hub(this happend to mine) there are no gear teeth as such,probably just a duff sensor if the reader says so. you don't say if the ABS warning light is constantly on this would tell you to get the car plugged in and read.
