Abstract: An apparatus having a plurality of components with printed circuit boards (PCB) having electronic circuits that act on electrical and/or electromechanical function elements is provided. The PCBs communicate with one another via a serial communication bus. The components have analog and digital signal generators allocated to them whose signals act on the PCBs as an input quantity. The PCBs have the capability for implementing self-tests. The self-tests provide test results that are supplied to a service computer as input quantities. Converters for the data for a transmission via a standard interface are provided for the transmission of the data onto the service computer. In an embodiment, the service computer has a first module with a diagnosis software component that enables an interactive error diagnosis off-line. The service computer also contains a second module that produces a connection between the first module and the apparatus components to enable an on-line diagnosis with the first module.