Abstract: A method is provided for monitoring vehicle function components using a diagnostic device taken along in the vehicle. A multiplicity of individual test routines are carried out, respectively, given the presence of start conditions specific to the test routine, in a fixed, cyclic sequence in order to obtain information on the presence or absence of a fault with respect to the relevant function components. Data relating to a first-time execution of a respective test routine is retrievably stored. With the aid of this data, before activation of a test routine pending according to a sequence provided it is determined given the presence of appropriate start conditions whether the test routine has already been performed at least once and whether at least one other activatable test routine exists which has not yet been performed. If no, the pending test routine is activated, otherwise, the test routine not yet performed is activated.

Abstract: The invention relates to a method for checking the operability of a cyclically controlled regeneration valve in a tank venting system of a motor vehicle which utilizes the realization that during operation of the system significant pressure variations are generated in a discharge line arranged between an adsorption filter and the regenerating valve whenever the duty ratio of the regeneration valve is within a certain range. If the regeneration valve is operated at such a duty ratio, the pressure variations in the discharge line are recorded and the extreme pressure valves are determined in an evaluation device for a specified time period after which the difference between the maximum and the minimum pressures is determined and if this difference is below a predetermined threshold, the regeneration valve is indicated as being defective.