Abstract: After the start of an internal combustion engine, a check is made to see whether a positive change in a measurement signal is established. A positive change is established if the measurement signal lies below a predetermined threshold value when the internal combustion engine is started. A fault entry is made if, within a predetermined time period, the positive change in the measurement signal, expressed as the difference between the measurement signal when the internal combustion engine is started and a present value of the measurement signal when the time period has elapsed, does not reach an expected value.

Abstract: The diagnostic process for use in evaluation of sensor signals, especially in evaluation of the output signals of a knock sensor in an internal combustion engine, includes determination of a reference level from the amplified sensor signal, which is compared with a predetermined lower and/or upper limiting value for error detection. An error is detected as a predetermined variation of the reference level from the limiting values. At least one of the limiting values is doubled and selection of the one or the other of the doubled threshold values occurs with the aid of predetermined conditions, e.g. of the internal combustion engine.

Abstract: A device for rejecting noise in an ion-sense ignition knock signal compares an integrated knock signal to a peak knock signal multiplied by a time factor to determine the presence of noise. A bandpass filter coupled to an engine's spark plug through ion-sensing circuitry generates a filtered knock signal. The filtered knock signal is passed through a rectifier to produce a rectified knock signal. The rectified knock signal is then passed through an integrator and a peak detector to produce an integrated knock signal and a peak knock signal, respectively. The peak knock signal is multiplied by a predetermined time factor and the result is compared to the integrated knock signal. If the result is less than the integrated knock signal, then no noise disturbance occurred and the integrated knock signal is passed on to a knock detector.

Abstract: A sensor tester for testing multiple vehicle sensors is provided comprising: a circuit for testing a vehicle piezoelectric knock sensor; a circuit for testing a vehicle speed sensor; and a circuit for testing ignition coils. The circuit for testing piezoelectric knock sensors comprises: an integrated circuit electrically connectable to a power source, the integrated circuit having a multiple step voltage divider, a connector for connecting the integrated circuit to the knock sensor; and a plurality of light emitting diodes electrically connected to the voltage divider of the integrated circuit.