It is known for a central electronic control unit in a motor vehicle to exchange data through a serial data bus with other control units, e.g. those for fuel injection, ignition timing, and braking. Prior art systems transmitted these data automatically, regardless of whether all these parameters were relevant to the actual operating state of the vehicle, thereby resulting in heavy loading of the serial bus. The present invention determines which parameters are irrelevant to the current operating state and suppresses transmission, or even calculation, of these irrelevant parameters.