Let's start with the dosing module or dosing valve (1) rather far back. Here AdBlue is added to the exhaust gas metered by the engine management up to about one liter per 1000 kilometres. Then follows an area where the pre-reactions take place described below in the video, even designed as a mixer in the picture below. Behind the SCR catalyst (3). Before that, a temperature sensor (2) and behind it (image below) a NO _X probe measures the success of the whole action.

The particulate filter (4) is upstream in the system uppermost. In the same housing in front the oxidation catalyst (5), the also brings a certain heating of the exhaust gas. Each a line before and after the particulate filter lead to a differential pressure valve that indicates required regeneration. In addition, two broadband lambda probes (6.7) are still installed here.

This is an AdBlue tank for a passenger car which holds up to about 30 litres. So a distance of at least 30,000 kilometres between two inspections is covered. To prevent for example plopping noises, it also has additional baffles of the same plastic. In principle, its ventilation could be laid open to the outside. Because that would spread unpleasant odors through the active ingredient there is for ventilating a particularly valve (yellow).