Vehicle Speed Sensor: Description and Operation

Vehicle Speed Sensor (VSS)
The PCM determines the speed of the vehicle by converting a pulsing voltage signal from the vehicle speed sensor (VSS) into miles per hour. The PCM uses this signal to operate the speedometer.

CIRCUIT OPERATION
With the starter switch in ON or START, the VSS receives power. For every rotation the VSS outputs four pulses to the engine (M/T) or powertrain (A/T) control module (ECM or PCM), and the speedometer to gauge speed.