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.

The sensor unit has a toothed wheel with 29 teeth and an inductive sensor.

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. The control module uses this change of polarity as a pulse sensor. The frequency of the pulses increases with the speed of the wheel.

With a multimeter set for AC voltage connected between the two leads of the sensor, a reading of 100 mVAC should be obtained when the wheel is rotated one revolution per second.

A wheel speed of 20 km/h gives about 5 VAC.

Fig 1: Identifying Distance Between Sensor And Toothed Wheel

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Fig 2: Circuit Diagram - Front-Wheel Sensors

Courtesy of SAAB-SCANIA OF AMERICA, INC.

The distance between the sensor and the toothed wheel should be 0.3-1.2 mm. This distance is adjustable .

The control module uses the frequency to measure the vehicle speed .