How It Works

The permanent magnet generates a magnetic field in the wheel speed sensor. The flux lines of the magnetic field run perpendicular to the sensor coating on the sensor element. The deflection of the flux lines by the increment gear induces fluctuations in the resistance of the thin, ferromagnetic coating of the sensor element.

Fig 1: Identifying E85 - Wheel Speed Sensor Function

Courtesy of BMW OF NORTH AMERICA, INC.

E85 - WHEEL SPEED SENSOR FUNCTION LEGEND

Index	Explanation	Index	Explanation
1	Increment gear	2	Evaluation electronics
3	Signals from wheel speed sensors	4	Permanent magnet
5	Magnetic field flux lines	6	Sensor element

The fluctuations in the resistance are converted into voltages by the sensor element. From these relatively small voltages (up to 100 mV), the evaluation electronics generate current pulses with a clearly different low/high level (7 mA and 14 mA, resp.). The sensor's supply voltage is 12 volts. The wheel speed sensors can generate signals between 0 and 2500 Hz.