Direct excerpt from the E Class handbook: "Vehicles equipped with a diesel particulate filter: if the vehicle is predominantly operated over short distances, malfunctions may arise during the automatic regeneration of the diesel particulate filter." This may result in fuel accumulation in the engine oil, potentially leading to engine failure. Consequently, if you regularly drive small distances, you ought to undertake a 20-minute journey on a freeway or rural road at least every 500 kilometres.
It is essential to sustain a continuous speed, avoiding stop-and-go driving in urban areas; thus, the preference for motorways or rural roads.