Wheel Speed Sensor: Description and Operation

Wheel sensors








There are four wheel sensors, one at each wheel. The wheel sensors supply the control module with information about the rotation speed, acceleration and retardation of each wheel. By recording the pulses, the control module can calculate the wheel speed.

The wheel sensors are active sensors. When the pulse wheel rotates, the sensor generates a pulsed current (quadratic wave) where the strength of the current depends on the position of the pulse wheel. The signals from the coils in the wheel sensors are then affected by a magnetic resistance element, which generates a current which changes between 7mA and 14mA, and whose frequency increases with speed.

On the front wheels, the pulse wheel is pressed onto the outer constant velocity joint and the wheel sensors are located radially in the shaft housing relative to the pulse wheel. On the rear wheels, the pulse wheel is pressed onto the hub and the wheel sensors are located axially relative to the pulse wheel. The rear pulse wheels can be replaced. Both the front and rear pulse wheels have 48 teeth. In the event of a fault in any of the wheel sensors the following systems will be disengaged or will not engage:

- ABS
- TRACS
- STC
- DSTC

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.