Vehicle Speed Sensor: Description and Operation
VEHICLE SPEED SENSORDESCRIPTION
The Vehicle Speed Sensor (VSS) consists of a reed switch built into the speedometer head. As the speedometer cable turns, the reed switch closes the circuit ground four times per revolution.
OPERATION
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.