Vehicle Speed Pulse
WARNING: This page is about a different car, the 2008 Acura TL and 2007 Acura TL. However, it is still accessible from the selected car via links, so may be relevant.
The vehicle speed pulse is sent by the ECM/PCM. The ECM/PCM receives a signal from the countershaft speed sensor, then processes the signal and transmits it to the speedometer and other systems.
Courtesy of AMERICAN HONDA MOTOR CO., INC.