a method is provided for diagnosing a fault in a selective catalytic reduction system having an electric driven transportation device that provide a mass flow of a diesel exhaust fluid into the selective catalytic reduction system . the method includes , but is not limited to applying an electric signal to the transportation device for establishing the mass flow , monitoring a parameter value of the electric signal , monitoring the mass flow provided into the selective catalytic reduction system caused by the transportation device when it is driven with the signal , determining , for the monitored mass flow , the difference between the corresponding parameter value , and a corresponding parameter value stored in a data map .