Procedures for diagnosing an exhaust gas treatment device, which is dosing a reagent into the exhaust gas area of a combustion process, whereby the reagent is brought up to a dosing pressure and subsequently dosed, at which the diagnosis is undertaken with the aid of an evaluation of a pressure drop of the reagent, and a device for implementing the procedure are suggested. After turning off the pump a pressure drop that occurs afterwards is evaluated. The evaluation of the pressure drop considers a leakage loss of the pump.