For the cleaning of modern diesel engines, car manufacturers rely on SCR catalytic converters to reduce nitrogen oxide (NOx) emissions. For this purpose, an aqueous urea solution is injected. During driving, especially short distances and under difficult driving conditions, the required high temperatures in the exhaust system are often not achieved. The result: The conversion to nitrogen (N2) and water (H2O) cannot be carried out in the best possible way. As a result, white crystalline deposits form in the urea dosing system and the SCR / SCRF catalytic converter, the NOx reduction does not work properly, and increased emission values are achieved. The result can be engine malfunctions and loss of performance.