Vehicle Speed Sensor (VSS) - 7.3L Diesel Only
WARNING: This page is about a different car, the 2002 Ford RV Cutaway, 2002 Ford Econoline, 2002 Ford E550 Super Duty, 2002 Ford E450 Super Duty, and 2002 Ford Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
The vehicle speed sensor (VSS) (model-dependent) is a variable reluctance sensor that sends an A/C frequency signal to the powertrain control module (PCM). The VSS sensor signal is used by the PCM to calculate vehicle speed in mph and determine shift scheduling and electronic pressure control.
For diesel applications the VSS is used for output speed sensing, supplying the PCM with transmission output speed. The PCM then sends the TCC pulse width modulated signals to smoothly engage the torque converter clutch.