Gauge Indication Systems: Speedometer
WARNING: This page is about a different car, the 2003 Mazda Tribute. However, it is still accessible from the selected car via links, so may be relevant.
The instrument cluster receives the vehicle speed from the powertrain control module (PCM) via the SCP (J1850) line. If the instrument cluster receives no signal the speedometer will default to 0.0 km/h (0.0 mph).