Speed sensor, rear wheel
The rear left wheel speed sensor sends wheel speed data to pin 7 on the control module. The sensor is grounded on pin 27.
The rear right wheel speed sensor sends wheel speed data to pin 29 on the control module. The sensor is grounded on pin 8.
The wheel speed sensor is integrated in the wheel hub. It comprises a proximity sensor and a toothed wheel with 29 teeth.
The proximity sensor works like a small alternator, the sine-wave voltage of which increases with increasing wheel speed. The sine-wave voltage alternates between positive and negative polarity, which is achieved by alternate teeth and gaps on the toothed wheel. By measuring the frequency, the control module can determine the speed of each wheel.
A wheel speed of 20 km/h (12.5 mph) will give approximately 0.8 V AC 70 Hz
The ESP control module uses information on wheel speed to calculate the speed of the wheels in relation to each other. If the difference exceeds the limits, the control module will compensate for this by requesting braking and/or lowered engine torque.