The vehicle speed sensor (VSS) is mounted to the transmission and produces an AC signal. The frequency of this signal is proportional to the speed at which the transmission output shaft rotates, which is proportional to the speed of the vehicle.

The AC signal produced by the VSS is amplified and converted by the VSS buffer module. The signal is supplied to the powertrain control module (PCM), the cruise control module and the speedometer by the VSS buffer module. The VSS buffer module produces the signal by opening and closing internal solid-state switches to ground.

The signal to the PCM, the cruise control and the speedometer pulses at a rate of 4,000 times per mile. The PCM, the cruise control and the speedometer internally convert the number of pulses per mile in order to determine vehicle speed.