Vehicle Speed Sensor: Description and Operation

The Vehicle Speed Sensor is an integral part of the speedometer assembly. The ECM applies and monitors a 12V signal to the sensor. When the drive wheels are turning, the sensor alternately grounds the circuit, creating a pulsing action that occurs 4096 times per mile. The ECM calculates vehicle speed based on the time between pulses. This input is used by the ECM for idle air and fuel control calculations.