DTC P0502: Vehicle Speed Sensor Low Output: Description
WARNING: This page is about a different car, the 2001 GMC Savana, 2001 Chevrolet RV Cutaway, 2001 Chevrolet Cutaway, and 2001 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
Vehicle Speed Sensor (VSS) assembly provides vehicle speed information to Powertrain Control Module (PCM). VSS assembly is a permanent magnet generator. VSS produces an AC voltage as rotor teeth on output shaft of transmission pass through sensor's magnetic field. AC voltage level and number of pulses increase as speed of vehicle increases. PCM converts pulsing voltage to vehicle speed. PCM uses vehicle speed signal to determine shift timing and Torque Converter Clutch (TCC) scheduling. DTC P0502 will set when PCM detects a low vehicle speed when there is a high engine speed in a drive gear range.