Speed Signal

The vehicle speed sensor in the gearbox sends a sin wave alternating voltage to the speedometer. The frequency of the voltage is proportional to the speed of the sensor spindle (16 Hz/sensor revolution) and the amplitude increases with the frequency.

The electronic speedometer processes the alternating voltage and generates a pulsed square wave signal (4.8 pulses/revolution of the drive wheel) which is proportional to the speed. This means that if the speed increases, the number of pulses in the same time period increases. This signal goes to pin 9 on the control module. The control module uses the speed signal together with signals from the fuel injectors to calculate the fuel consumption.