Speedometer Head: Description and Operation

A Vehicle Speed Sensor (VSS) signal is supplied by the Powertrain Control Module (PCM) via discrete inputs. The vehicle speed data is sent from the PCM to the IPC through a class 2 serial data message. The VSS discrete signal is pulled up to ignition voltage in the PCM. The IPC uses the VSS data received from the PCM and a software program to determine the proper vehicle speed to display.