DTC P0502: Vehicle Speed Sensor Low Output: Description
WARNING: This page is about a different car, the 2003 Cadillac Seville and 2003 Cadillac DeVille. 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 (TCC) 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.