A method for diagnosing a metering system and device for carrying out the method

A method for the diagnosis of a metering system which meters a reagent (12) into the exhaust gas passage of an internal combustion engine, wherein the in a tank (10) mounted reagent (12) from a pump (14) is brought to an operating pressure (p0), wherein a return line (24) of the reagent (12) from the pump (14) is provided in which an electrically controlled metering valve (16), a flow rate is adjusted and in which (the pressure (p) of the reagent (12) between the pump 14) and the metering valve (16) is measured, wherein the return (24) of the reagent (12) is variably predetermined by means of an electrically controlled throttle (26), wherein the (pressure p) of the reagent (12) to a diagnostic starting pressure (pD) is placed, wherein the throttle (26) closed and thus the return (24) in which a Diagnosedosierrate is set, wherein the pump (14) is switched off is prevented, and in which then the measured pressure drop (40, 42, 44, 50, 52, 54) is checked to - if the pressure drop (40, 42, 44, 50, 52, 54) is outside a tolerance band (48) lies or is checked to - if the pressure drop (40, 42, 44, 50, 52, 54) is located above an upper limit or is checked to - if the pressure drop (40, 42, 44, 50, 52, 54) is below a lower limit value and is is provided in which an error signal at an established tolerance band limit value is exceeded, or (F), characterized in that the tolerance band (48) or a threshold value depending on the Diagnosedosierrate be set at least.