Silhouette V6-191 3.1L VIN D TBI (1995)
Vehicle Speed Sensor: Description and Operation
Circuit Operation
The Vehicle Speed Sensor (VSS), mounted to the Transaxle, produces an AC signal in the form of a sine wave. The frequency of this sine wave is
proportional to the speed at which the Transaxle rotates. The speed at which the Transaxle rotates is proportional to the speed of the vehicle.
For VIN D vehicles, the AC signal produced by the Vehicle Speed Sensor is amplified and converted to a square wave by the Vehicle Speed Sensor
Buffer. The square wave signal is supplied to the Powertrain Control Module (PCM), Cruise Control Module and Speedometer by the Vehicle Speed
Sensor Buffer. The Vehicle Speed Sensor Buffer produces the square wave by opening and closing internal solid state switches to ground. For VIN L
vehicles, the Vehicle Speed Sensor supplies a square wave directly to the PCM and the PCM supplies a signal to the Speedometer.
For VIN D vehicles, the square wave to the PCM is at a rate of 2000 pulses per mile while the Cruise Control Module and Speedometer see a square
wave at 4000 pulses per mile. The PCM, Cruise Control Module and Speedometer internally convert the number of pulses per mile per second to
determine vehicle speed. For VIN L vehicles, the PCM sends a square wave to the Speedometer at a rate of 4000 pulses per mile.
