Abstract: An on-board diagnostic arrangement is disclosed for checking component systems of a motor vehicle by test functions which are triggered during operation of the motor vehicle under predetermined start conditions. The test functions are characterized in that at least one signal can be coupled into the arrangement via which the triggering of the test functions by the arrangement is inhibited and in that at least one test function, which is carried out by the arrangement, is triggered independently of the predetermined start conditions and/or can be modified in its sequence. The arrangement makes possible a shortening of the check of component systems at the end of an assembly line or after customer service because satisfying time-consuming start conditions for the normal operation of the test functions can be omitted.

Abstract: Fluctuations of engine speed in the frequency range from 2 to 8 Hz, which produce "bucking" behavior of a motor vehicle, are detected by passing engine speed signals through a filter which reduces and delays the oscillations and a difference signal is then produced between the original and the processed speed signal in order to derive an alternating signal in the form of a square wave indicating the sign of a correction to be made to engine ignition timing for counteracting the bucking oscillations of engine speed. The square wave determines the sign of an anti-bucking ignition timing correction factor, of which the absolute value may be constant or may vary according to the sign of the correction and, if desired, also in accordance with engine operation parameters.