Vehicle Speed Sensor: Description and Operation

Vehicle Speed Sensor Circuit:

PURPOSE
The sensor is used by the Engine Control Module (ECM) to determine vehicle speed and by the speedometer to drive the trip odometer/mileage odometer stepper motors and the speedometer driver to indicate vehicle speed.

OPERATION
The speed sensor is a `quenched oscillator' pulse generator which provides approximately 4000 pulses per mile. The speed sensor pulses the signal wire, switching its connection to ground on and off. The number of pulses increasing with vehicle speed.