Hall-effect Sensor

It is used for crankshaft, camshaft and wheel speed sensing. It needs a power supply, usually 5 or 12 V. It gives a square wave even at very low speed. Many modern wheel speed sensors are active Hall or magnetoresistive sensors that can even detect direction of rotation. Their signal is often a current that switches between two levels, read by the ABS module.

A magnetic field changes the voltage across a semiconductor chip.

Lost supply or ground stops the signal. Metal debris on the tip can corrupt the reading.