Automotive tech can be puzzling. To ease the confusion, each month we explain how a component in your vehicle works
A wheel-speed sensor is an inductive pick-up that sends pulses to the ABS control unit to calculate wheel speed in real time. The electric pulses are generated when a perforated ring or metal teeth passes close to the sensor. The number of teeth per revolution (as well as wheel sizes) is stored and available to the ABS control unit as part of the input to the calculations. All four wheels’ speeds are needed for ABS and electronic stability control functionality. The vehicle speed is usually calculated as the average of all four sensor values to still be accurate around bends where individual wheel speeds differ. A faulty wheel-speed sensor is the most common fault present when the ABS light is on in the instrument cluster. Using a specialised diagnostic scan tool, all four vehicle-speed values can be read from the CAN bus of a vehicle through the diagnostic OBD port to aid the fault-finding process.