ABS Kicks in at low speed stops?

Since the circuit is good enough to read at all it is not likely to be faulty. Not reading the signal at low speed is more consistent with bearing failure on the front wheel hub. It could also be accompanied by a speed related hum or growl noise that may get louder when turning. It is wise to jack that wheel off of the ground and check the wheel bearing for play/ wear, check side to side and up and down, there should be little to no movement. I recommend both sides at the same time and be sure to check the alignment. New hubs come with the sensor anyway and a bad alignment can ruin new bearings. I replace a lot of Explorer wheel bearings and rarely if ever the sensor alone. The sensor is integrated with the sealed hub unit and factory shimmed. Hope this helps.