Methods for monitoring the catalytic activity of a catalytic converter

Abstract

Two methods are provided for monitoring the catalytic activity of a catalytic converter arranged in the exhaust gas conduit of a motor vehicle. According to one method, proceeding from a cold start, a temperature progression is determined by a temperature sensor arranged downstream of the catalytic converter and a temperature plateau is thereby determined; the length of the temperature plateau is compared with the length of a temperature plateau determined in advance on a new catalytic converter; a shortening of the length of the measured temperature plateau is interpreted as an aging of the catalytic converter; and the catalytic converter is judged as defective if the shortening exceeds an established limiting value. According to a second method, two temperature sensors are used, one upstream and one downstream of the catalytic converter, with temperature progressions being recorded at both, and temperature differences between the first and second temperature sensors are determined at the beginning and at the end of a temperature plateau established by the second temperature sensor. The differences are offset against each other, and the offset value is compared with a reference value from a new catalytic converter.