Output Speed Sensor (OSS)
WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
The automatic transmission output shaft speed (AT OSS) sensor is a three-wire magnetic pick-up sensor that is mounted externally to the transmission. The OSS utilizes the gear teeth, located on the output shaft, to generate a voltage signal of varying frequency that corresponds to the rotational speed of the output shaft. The OSS signal is sent to the PCM and is used to calculate the vehicle speed. Simultaneously, the automatic transmission input shaft speed sensor (AT ISS) signal is used to calculate the vehicle speed. The PCM compares the vehicle speed calculated from both speed sensors and uses this comparison for diagnosis of the speed sensors.