The voltage switches between 0.7v and 1.7v as the magnetic reluctor segments pass the sensor. If you get 48 of them for each revolution of the wheel (mark the tyre with chalk) then both sensor and reluctor are good.
If missing segments are random suspect the sensor and if they are in the same part of the revolution each time suspect the reluctor.
For by far the vast majority of ABS faults you don't need any fancy diagnostic equipment - just a voltmeter.
