Vehicle Speed Sensor: Description and Operation

Vehicle Speed Sensor (VSS):

The Vehicle Speed Sensor, mounted to the Transmission, 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 Transmission rotates. The speed at which the Transmission rotates is proportional to the speed of the vehicle.
The AC signal produced by the Vehicle Speed Sensor is amplified and converted to a square wave by the Vehicle Speed Sensor Module. The Vehicle Speed Sensor Module produces the square wave by opening and closing internal solid state switches to ground. The square wave signal is supplied to the Engine Control Module (ECM), Cruise Control Module, Audio Alarm Module, Power Steering Control Module (Sedan), and Speedometer by the Vehicle Speed Sensor Module. The square wave to the ECM is at a rate of 2000 pulses per mile, while the Cruise Control Module, Audio Alarm Module, Power Steering Control Module (Sedan), and Speedometer see a square wave at 4000 pulses per mile. The ECM, Cruise Control Module, Power Steering Control Module (Sedan), and Speedometer internally convert the number of pulses per mile per second to determine the vehicle speed.