Abstract: The invention is directed to a method of checking the tightness of exhaust valves of an internal combustion engine with the aid of an apparatus. The apparatus includes a device for forming a value LU for the uneven running of the engine and a device for metering air into a region disposed downstream of the exhaust valves as viewed in the flow direction of the exhaust gas. In the method, a first value LU1 is formed for the uneven running without air being supplied in the above-mentioned region and a second value LU2 is formed for uneven running with air being supplied in the above-mentioned region. An exhaust valve is deemed to leak when the first and the second values for the uneven running differ by more than a predetermined amount.

Abstract: A system and method for generating a signal which indicates whether a motor vehicle containing such a system is operating on a rough road surface. The generated signal is based on the signals output by a sensor that measures the air-mass flow rate through the air-intake manifold of an internal-combustion engine. The system and method use the differences in the signals output by the sensor when on a smooth road surface and a rough road surface to generate the signal indicative of a rough road surface. The rough road indication signal can be applied, inter alia, to engine misfire detection, anti-lock braking control, and vehicle chassis regulation.

Abstract: The invention is directed to a method for obtaining a value for evaluating the performance loss of a catalytic converter with the aid of a forward signal of a forward gas probe mounted forward of the catalytic converter and a rearward signal of a rearward gas probe mounted rearward of the catalytic converter, the catalytic converter being connected to an internal combustion engine. The method includes the steps of: carrying out the method during the steady-state operation of the engine; multiplying the forward signal and the rearward signal with each other to form a plurality of products; averaging the products over a plurality of oscillations of the forward signal to obtain a mean value; and, utilizing the mean value as a value for evaluating the performance loss of the catalytic converter. This correlation method can be varied in different ways and especially in that the forward-probe signal is correlated without or with phase shift with the rearward-probe signal.

Abstract: The invention relates to a method and an arrangement for checking the operability of an electric heater in motor vehicles and especially the heater of an oxygen probe which is mounted in the exhaust gas channel of an internal combustion engine. It is necessary to determine the temperature-dependent electrical resistance and the temperature of the oxygen probe heater for a precise evaluation of the operational state of the oxygen probe heater. The basic principle of the invention is based upon the consideration that the measurement of the electrical resistance of the oxygen probe heater is then carried out when the oxygen probe heater has cooled down to the ambient temperature. Whether this cool down has taken place can be determined in various ways in accordance with the invention, for example, from the cool down of the engine block or by a comparison of the engine block temperature to the intake-air temperature.