Wheel Sensors
The wheel sensors are installed on the spindle joints of the front and rear wheels. The wheel sensors are active sensors. The task of the wheel sensors is to supply the control module information on the rotation speed of each wheel. The control module uses the signals from the wheel sensors to calculate wheel speed and the acceleration and retardation of the car.
The wheel sensors are supplied with 12 V. When the magnetic pulse wheel rotates, the sensor generates a pulsed current (quadratic wave). The strength of the current depends on the position of the pulse wheel. The signals from the coil in the sensor are then affected by the resistor, which is sensitive to magnetic fields. This means that the output signal is a current which oscillates between 7 mA and 14 mA. The frequency increases with speed.
The magnetic pulse wheel is integrated into the inner wheel bearing seal and the front wheel sensor is radially positioned in the shaft housing in relation to the magnetic pulse wheel. The rear wheel sensors are axially positioned in relation to the magnetic pulse wheel. Both the front and rear magnetic pulse wheels have 88 poles, 44 north poles and 44 south poles. In the event of a fault in any of the wheel sensors the following functions do not engage or are disengaged:
- Anti-lock brake system (ABS)
- Stability control (SC)
- Traction control (TC)
- Active yaw control (AYC).
Electronic brake force distribution (EBD) is available if one wheel sensor is faulty. Electronic brake force distribution (EBD) is disengaged if there is a fault in more than one wheel sensor simultaneously.
The control module calculates the vehicle speed using the signals from the wheel sensors.
There are diagnostics for the wheel sensors.