The invention relates to a method for detecting an error in a component assembly of a motor vehicle, the component assembly having a functional control unit and at least one function module to be controlled by the functional control unit as components. The protective guide includes a flexible curved strip-shaped base and a plurality of flexible sectioning members. A counter counts incoming clocks and times out after a fixed number of vibrator oscillations. Each level contains information from different levels of slivers of the circular space. The invisible information recording part is, for example, a magnetic recording layer, a write-once optical recording layer or an integrated circuit memory, in which information can be recorded and erased. The coupling element can be eliminated if the optical waveguide is directly aligned on the submount.