Vehicle Speed Sensor: Description and Operation

Vehicle Speed Sensor (VSS):

The Vehicle Speed Sensor (VSS) provides information to the ECM for control of idle speed and transmission converter clutch engagement as well as controlling canister purge of the fuel evaporative emission system. This signal is generated by a reed switch and magnet that is built into the speedometer. As the magnet turns with the speedometer cable, its magnetic force causes the reed switch to turn "ON" and "OFF." The VSS sends a pulsing voltage signal to the ECM, which the ECM converts to miles per hour.