Vehicle Speed Sensor: Description and Operation

The vehicle speed sensor generates a signal which indicates the vehicle speed to the speedometer. The speedometer consists of a vehicle speed sensor, an ammeter (needle movement), stepper motor (odometer), and a driving circuit (printed circuit board).

The vehicle speed sensor is mounted to the transmission. The transmission pinion shaft rotates and generates four pulses per one rotation. The rate at which the pulses are generated indicates the vehicle speed. The vehicle speed sensor (incorporated in the speedometer) uses the pulses to control needle movement and sends vehicle speed information to the engine or powertrain control module (ECM or PCM) and the cruise control unit. The speedometer sends 4096 pulses per mile and the frequency indicates the vehicle speed.