Vehicle Speed Sensor: Description and Operation
Vehicle Speed SensorPURPOSE
The Vehicle Speed Sensor (VSS) reports road speed to the Engine Control Module (ECM). This information is used to synchronize emission systems and to adjust for various engine demands.
OPERATION
The sensor is a reed switch that is controlled by a rotating magnet. As the magnet passes under the sensor the contacts close momentarily, resulting in a ground signal. The frequency of these ground signals sent to the ECM is relevant to vehicle speed.