F 250 4WD Super Duty V10-6.8L VIN Z CNG (2003)
Vehicle Speed Sensor: Description and Operation
Vehicle Speed Sensor (VSS)
The vehicle speed sensor (VSS) is a variable reluctance or Hall-effect sensor that generates a waveform with a frequency that is proportional to the speed
of the vehicle. If the vehicle is moving at a relatively low velocity, the sensor produces a signal with a low frequency. As the vehicle velocity increases,
the sensor generates a signal with a higher frequency. The PCM uses the frequency signal generated by the VSS (and other inputs) to control such
parameters as fuel injection, ignition control, transmission/transaxle shift scheduling and torque converter clutch scheduling.
For F-Series and Excursion, the VSS signal is generated by the Generic Electronic Module (GEM). The GEM generates VSS from a speed sensor on the
rear axle.
