Metro L4-079 1.3L VIN 9 TBI (1995)
Vehicle Speed Sensor: Description and Operation
Vehicle Speed Sensor (VSS) (M/T Only)
DESCRIPTION
The Vehicle Speed Sensor (VSS) consists of a reed switch built into the speedometer head. The Engine Control Module (ECM) applies 5 volts to
the VSS.
OPERATION
As the speedometer cable turns, the reed switch closes the circuit to ground four times per revolution of the speedometer cable. As vehicle speed
increases, the frequency of ground pulses received by the ECM also increases. Therefore, by calculating the frequency of the ground pulses, the
ECM is capable of determining vehicle speed.
