Output Shaft Speed (OSS) Sensor
WARNING: This page is about a different car, the 2012 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.
The Output Shaft Speed (OSS) sensor is a Hall-effect pickup, located on the transfer shaft drive gear, that sends a signal to the PCM to indicate transmission output speed. The OSS is used for TCC control and shift scheduling.