Vehicle Speed Sensor: Description and Operation

The Vehicle Speed Sensor generates a signal that is proportional to vehicle speed. The signal produced is a sine wave, which the PCM processes into a square wave to supply inputs to the Speedometer, Passive Restraint Timer Module, and the Computer Command Ride (CCR) Controller.
The PCM takes the sensor/voltage pulses from the Vehicle Speed Sensor, through the PPL (401) and YEL (400) wires, and uses them to close solid-state output switches. The output terminals are switched to ground at a rate that is proportional to vehicle speed. The Speedometer, CCR Controller and Passive Restraint Timer Module (if equipped) are switched at te same frequency that the PCM generates: 4000 pulses per mile.