Analog

The 4 wheel sensors are used to determine vehicle speed and the degree of slip/spin at the rear wheels.

These inductive type sensors are installed "in line" with the rotating teeth of an impulse wheel. The "negative" side of each sensor (connected to B-) is also used as a shield to prevent the induction of foreign signals to the control unit.

As the impulse wheel rotates, each tooth of the wheel that passes the sensor causes an AC voltage to be produced by the sensor. The ASC (+T) control unit interprets the wheel speed from the number of pulses per second produced by the AC voltage.

The sensor must be clean (free of metal chips, etc.) and properly mounted with the designed clearance to scan the impulse wheel. The impulse wheel must also be clean, securely mounted, with the teeth intact.

Each sensor can be checked:
Statically
^ short to ground
^ short to B+
^ resistance
^ inductance

Dynamically
^ AC voltage
^ frequency
^ oscilloscope pattern