Vehicle Speed Sensor: Description and Operation

Vehicle Speed Sensor (VSS) For M/T
The speed sensor consists of the reed switch and magnet. It is built in the speedometer. As the magnet turns with the speedometer cable, its magnetic force causes the reed switch to turn ON and OFF. Such ON/OFF frequency increases or decreases in proportion with the vehicle speed and is sent to ECM (PCM) as pulse signals.

ECM (PCM) uses it as one of the signals to control various devices.




Vehicle Speed Sensor (VSS) For A/T
The vehicle speed sensor consists of a magnetic core with magnet and coil. It is mounted on transmission case with 0.6 mm (0.024 in.) air gap between the core end and countershaft gear tooth.

While the countershaft rotates, magnetic flux is cut by gear tooth thus a pulse is generated in the sensor coil according to the speed. And then, the pulse is transmitted to powertrain (engine) control module as speed signal.