Vehicle Speed Sensor

Transmissions have input and output speed sensors so the control unit can time shifts and detect slipping. Many cars take vehicle speed from the ABS wheel speed sensors instead of a dedicated sensor. Speed data is shared over the car’s network, so one faulty sensor can affect the speedometer, cruise control, shifting and stability systems.

Cars use several speed sensors: wheel speed sensors for ABS, input and output shaft sensors in the transmission and sometimes a separate vehicle speed sensor. Speed signals are shared between many systems over the car’s data network. The speedometer, odometer, cruise control, power steering assistance, transmission shift timing and stability control can all depend on the same wheel or output shaft signals, which is why one sensor fault can affect several functions at once.

Most are Hall-effect or inductive sensors reading a toothed ring. The pulse frequency rises with speed. Most are magnetic or Hall-effect sensors that read a toothed ring or magnetic encoder.

Faults cause harsh or erratic shifting, a dead speedometer and codes such as P0500 or P0715. A faulty speed sensor can cause a dead speedometer, erratic shifting, cruise control problems and ABS or traction control warnings.