Abstract

An exhaust gas system for a multi-cylinder internal combustion engine, in which some cylinders are adapted to be effectively disconnected; the exhaust gas system includes in a common exhaust line, an O2 -probe and two series-connected catalysts while a separate exhaust gas line is coordinated to the cylinders adapted to be effectively disconnected; a control member operable as a function of load opens three separate branch connections from the separate exhaust line to the common exhaust line in such a manner that when all cylinders are firing, the branch connection terminating upstream of the O2 -probe is opened; the branch terminating in the common exhaust line between the O2 -probe and the first of the series-connected catalysts is opened when at least one of the cylinders is effectively disconnected and when the internal combustion engine is still relatively cold or warms up to a middle temperature; at temperatures exceeding the middle operating temperature, the branch connection terminating between the two catalysts is opened.