Vehicle Speed Sensor: Description and Operation

PURPOSE/OPERATION
Vehicle speed sensor 2 provides vehicle road speed information to the ECM. The ECM uses this data to properly determine ignition and fuel delivery curves. The sensor consists of a reed switch and magnetic rotor turned by the speedometer cable. One rotation of the magnetic rotor opens and closes the reed switch four times, producing a digital signal which is converted to vehicle speed by the ECM. The sensor operates whenever the vehicle is moving with ignition ON. As the transmission rotates, the speed sensor sends a pulsed on/off signal to the ECM.