Speedometer with odometer and trip meter (TC/ABS): Speedometer
The main instrument unit has an electronic speedometer. The TC/ABS control module receives speed information from all the wheel speed sensors. The information is processed and sent continuously to the P-bus. The main instrument unit reads the speed information from the rear left wheel and converts it to km/h. Information from the rear right wheel will be used if information from the rear left wheel is missing.
The information from the wheel sensors to TC/ABS is a square wave pulse that varies periodically between B+ and 0V. This takes place 29 times per wheel revolution.
With the wheels stationary, the voltage may be either B+ or 0 V.
The speedometer stepping motor is pulsed and controlled internally by the main instrument unit control module, which also forwards the speed information to the bus.