Self-Test Output/Self-Test Input (STO/STI) Connectors
WARNING: This page is about a different car, the 1994 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.
The STO connector is a 6-pin connector used to perform self-test diagnostic procedure. The STI is a single-pin connector, located next to STO. When STI is grounded, it activates fault code output function. Codes are retrieved through STO connector.