Principles of Operation: Speedometer/Odometer
WARNING: This page is about a different car, the 2005 Mercury Sable and 2005 Ford Taurus. However, it is still accessible from the selected car via links, so may be relevant.
The instrument cluster receives the vehicle speed sensor (VSS) signal from the PCM via the CAN circuits. The instrument cluster monitors the VSS input from the PCM and commands the speedometer with a corresponding movement of the pointer.