Each sensor has a connector which can go open circuit and cause problems. They are usually situated only a short distance from the sensor itself. What to do is open the connector then apply a moisture repelent and refit. Another problem with ABS systems on the 850's is that road dirt and grease can fill the gap between the castleations on the encoder wheel. This then sends a low amplitude signal to the processor which can think that the wheel has stopped and or give a warning lamp on(MIL). Best thing to do is to clean all the encoders thoroughly and the sensor itself. Hope that has been of some use.