DTC P0502: Vehicle Speed Sensor Circuit - Low Input: Description
WARNING: This page is about a different car, the 2002 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
The Vehicle Speed Sensor (VSS) is a permanent magnet generator attached to the transmission case. The final drive assembly has a toothed wheel, VSS rotor. As the final drive assembly rotates, an AC voltage is induced and transmitted to the PCM. The PCM converts the AC voltage into a digital signal. The PCM uses the vehicle speed to determine shift timing, torque converter clutch apply and release, and gear ratio. If the PCM detects a low vehicle speed and a high transmission input shaft speed while in a drive range, then DTC P0502 sets.