October 30: LEMON manuals on a temporary server, it is slow and having issues, download the manuals you need! Later in November we will switch back to the fast server.

Vehicle Speed Sensor

Vehicle Speed Sensor (VSS) consists of a reed switch built into speedometer head. ECM supplies VSS with a 5-volt reference signal. As speedometer cable rotates, the reed switch closes the circuit to ground 4 times per revolution. As vehicle speed increases, frequency of ground pulses increase. This pulse is sent to ECM and interpreted as vehicle speed.