Front-wheel sensors: Notes
The front left wheel sensor sends a wheel-speed signal to pin 7 on the control module. The sensor is grounded via pin 6.
The front right wheel sensor sends a wheel-speed signal to pin 5 on the control module. The sensor is grounded via pin 3.
Mounted on the right-hand and left-hand outer drive shaft universal joints is a toothed wheel with 29 teeth. A sensor of inductive type is mounted on each steering swivel member. The gap between sensor and toothed wheel should be 0.3-1.3 mm and is not adjustable.
The inductive 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 2 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 a change in engine torque.