Speedometer with odometer and tripmeter (TC/ABS and ESP): Speedometer
The main instrument unit is fitted with an electronic speedometer. The TC/ABS or ESP control module receives the speed information from all wheel sensors. The information is processed and sent continuously to the P bus. The main instrument unit reads the information on the speed from the left rear wheel and converts this to km/h. If information from the left rear wheel is absent, information from the right rear wheel is used.
Information from the wheel sensors to the TC/ABS or ESP control module is a square wave pulse which varies periodically between B+ and 0 V. This change occurs 29 times per wheel revolution.
With the wheels stationary, the voltage may be either B+ or 0 V.
The speedometer stepper motor is pulse-controlled and controlled internally from the main instrument unit control module which sends information on the speed to the bus.