Vehicle Speed Sensor: Description and Operation

VSS Buffer Circuit Wiring Diagram:

NOTE: Because different models and engine applications vary in wire colors, circuit numbers, and pin numbers, the above image is a typical example. Refer to COMPUTERS AND CONTROL SYSTEMS/SCHEMATIC AND ROUTING DIAGRAMS for specific schematic applications.

PURPOSE:
The Vehicle Speed Sensor (VSS) is made up of a coil, which is mounted on the transmission, and a tooth rotor which is mounted to the output shaft in the transmission. As each rotor tooth nears the coil, the coil produces an Alternating Current (AC) voltage pulse. As the vehicle speed increases, the number of AC voltage pulses increase. The VSS signal buffer processes inputs from the VSS and output signal to the speedometer control module, and cruise control module. The VSS buffer signal takes the voltage pulses from the VSS and uses them to open and close four solid state output switches to ground at a rate proportional to vehicle speed. The VSS buffer is matched to the vehicle based on final drive ratio and tire size. It is important to ensure that the correct VSS buffer is installed in the vehicle if replacement is necessary.