Main instrument unit, detailed description: Speedometer
Information on speed is generated in TCS or ESP active wheel speed sensor (rear left on petrol cars and front left on diesel). The TCS/ESP control module converts the speed signal (48 pulses/rev) to wheel speed.
The speed signal is transmitted as RPM on the P-bus and is converted by the engine control module to vehicle speed after allowing for the programmed tire dimension.
The engine control module (ECM) transmits the vehicle speed on the P-bus. CIM forwards the vehicle speed to the I-bus. The main instrument unit shows the vehicle speed on the speedometer. The control module transmits the vehicle speed on the I-bus, where information is made available to all the control modules.