Vehicle Speed Sensor: Description and Operation

PURPOSE
Vehicle speed information is provided to the Electronic Control Module (ECM) by the Vehicle Speed Sensor (VSS) which uses a Permanent Magnet (PM) generator and it is mounted in the transaxle.

OPERATION
The PM generator produces a pulsing voltage whenever vehicle speed is over about 3 MPH. The AC voltage level and the number of pulses increases with vehicle speed. The ECM then converts the pulsing voltage to MPH which is used for calculations, and the MPH can be displayed with a "SCAN" tool. Output of the generator can also be seen by using a digital voltmeter on the AC scale while rotating the generator.
The function of Vehicle speed Sensor (VSS) buffer used in past model years has been incorporated into the ECM. The ECM then supplies the necessary signal for the instrument panel (4000 pulses per mile) for operating the speedometer and the odometer.