Speedometer with odometer and trip meter: Speedometer
The main instrument unit is fitted with an electronic speedometer. The ABS control module receives information on vehicle speed from the rear left-hand wheel speed sensor. This information is processed and conveyed continuously to terminal 10 (K12) of the main instrument unit's control module.
The information, in the form of a square wave pulse, varies periodically between B+ and 0V. The main instrument supplies the current and the ABS control module grounds the output. This takes place 29 times per wheel revolution.
With the wheels stationary, the voltage may be either B+ or 0 V.
The main instrument unit uses the frequency to calculate the vehicle speed.
The speedometer is powered and controlled by the main instrument unit control module, which converts the frequency modulated signal to km/h or mph. A correction is made depending on the programmed tire size, whereby the speed information is put on the bus.