my opinion is based on cars that i work on. as soon as the abs module sees trouble front or back it will set a code and quit working. probably for safety reasons. a lot of times i see the wires cut because some one was changing a tire and when they through the tire on it cuts the wires on top of the upper a frame. also when the bearings fail it sometimes grinds off the end of the sensor. i changed a front wheel bearing and it had the trigger mechanism in the bearing and it was defective and it gave all kinds of bad readings bought a dealer bearing and all was good.