If the sensor has several years on it, just replace it. The sensor is essentially an iron core with a LOT of fine copper wire wound around it. The coil senses the changes in the magnetic field caused by the tone ring. If any moisture at all gets into the core (osmotic moisture incursion through the plastic does it; salt does not help) then the core rusts and can kill the coil. The expansion caused by the rusting also serves to wedge the <bleep>ing sensor in the hole in which it resides and makes removal a <difficulty>.
Fortunately, the sensors, unique to each side in front, are not terribly expensive, but the r&r is, given the labor that will be required for removal.
Good luck. It is not pleasant this time of year, if your weather is like ours is just now. Hopefully you at least have a garage in which to do the job.
Cheers,
PH