Speedometer Module: Description and Operation

The Vehicle Speed Sensor (VSS) generates a signal that indicates the speed of the solid state PCM to supply inputs to the Cruise Control Module, Speedometer and Odometer.

The Vehicle Speed Sensor is mounted in the Transaxle. A magnet rotates near a coil, producing voltage pulses in the coil. The frequency of the AC voltage coming from this coil depends on the vehicle speed. The VSS sends pulses to the PCM at the rate of 40,000 pulses per mile.

The PCM takes the voltage pulses from the sensor and uses them to close a solid state output switch. The output terminal is switched to ground at a rate that is proportional to the speed of the vehicle. The Speedometer and Odometer are switched at 4,000 pulses per mile.