DTC P0502: VSS Circuit - Low Input (M/T): Description
WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
Output Speed Sensor (OSS) produces an AC voltage of different amplitude and frequency depending on the velocity of the output shaft. OSS produces signal from evenly spaced machined notches on transaxle final drive assembly. OSS produces a readable AC voltage signal when speed is more than 3 MPH. OSS signal is sent to ECM, which is used to determine vehicle speed. DTC sets when ECM does not detect an OSS signal for a certain length of time.