Output Shaft Speed (OSS) Sensor
WARNING: This page is about a different car, the 2004 Mercury Monterey and 2004 Ford Freestar. However, it is still accessible from the selected car via links, so may be relevant.
The output shaft speed (OSS) sensor is a magnetic pickup, located at the output shaft ring gear, that send a signal to the powertrain control module (PCM) to indicate transmission output speed. The OSS is used for torque converter clutch control, speed scheduling and to determine electronic pressure control.