Abstract: A method and an apparatus for determining the fill level of a fluid (2) in a tank (1), wherein a propagation time of an ultrasonic signal between an ultrasound element (4) and a reflection at the surface (3) of the fluid (2) is measured. A first, single reflection and a second, double reflection are evaluated, wherein the measurement of the reflections is carried out with a measurement setting with an excitation energy of the ultrasonic signal and a sensitivity. The sensitivity is indicated by a gain and a comparison value (13). Via measurements with different measurement settings, a suspected first reflection and a suspected second reflection are located and a plausibility check is carried out of the propagation times of the first and second reflections with respect to each other.

Abstract: A method for diagnosing a quality signal (26). The quality signal (26) is provided by a quality sensor (24) used in a reagent metering system (10). The reagent metering system (10) meters a urea/water solution (14) stored in a tank (12), the quality of which is checked by the quality sensor (24), upstream of an SCR catalytic converter (20).

Abstract: A method for diagnosing a quality signal (26). The quality signal (26) is provided by a quality sensor (24) used in a reagent metering system (10). The reagent metering system (10) meters a urea/water solution (14) stored in a tank (12), the quality of which is checked by the quality sensor (24), upstream of an SCR catalytic converter (20).