Vehicle Speed Sensor: Description and Operation

Vehicle Speed Sensor (VSS) (M/T Only):

DESCRIPTION
The Vehicle Speed Sensor (VSS) consists of a reed switch built into the speedometer head. The Engine Control Module (ECM) applies 5 volts to the VSS.

OPERATION
As the speedometer cable turns, the reed switch closes the circuit to ground four times per revolution of the speedometer cable. As vehicle speed increases, the frequency of ground pulses received by the ECM also increases. Therefore, by calculating the frequency of the ground pulses, the ECM is capable of determining vehicle speed.