Exhaust gas systems of internal combustion engines may be designed as dual flow, i.e., having two separate exhaust gas lines carrying the exhaust gases away from the internal combustion engine in parallel.  For example, dual-flow exhaust gas systems are expedient with V-type engines to remove the exhaust gases from the two cylinder banks separately.  In addition, to reduce emissions of pollutants, it is customary to provide the exhaust system with exhaust gas purification devices such as catalytic converters and particulate filters.  To check proper functioning of such exhaust gas treatment devices, a corresponding sensor and/or a corresponding probe can be provided in the exhaust line downstream from the respective device.  With the help of this probe and/or sensor, for example, the residual presence of certain pollutants in the exhaust gas may be detected.  This function test is of growing importance in catalytic converter arrangements in which a catalytic converter having selective catalytic reduction, referred to with the abbreviation SCR catalytic converter, follows an oxidation catalyst, whereby ammonia or urea which is converted to ammonia because of the high exhaust temperatures, is introduced upstream from the SCR catalytic converter.  With the help of a corresponding sensor, it is thus possible to ascertain downstream from the catalytic converter arrangement whether a residual amount of ammonia or urea is contained in the exhaust.  Depending on this measurement, proper functioning of the catalytic converter arrangement can be evaluated.  If necessary, it is also possible to intervene in the control or regulation of the catalytic converter arrangement accordingly. 
In the case of dual-flow exhaust systems which contain a separate catalytic converter arrangement in each exhaust line, it is fundamentally possible to arrange a corresponding probe in the exhaust line downstream from the respective catalytic converter arrangement.  Such probes or sensors are comparatively expensive, however, in particular the associated expense for installation and for the analyzer circuits.