Method and apparatus for controlling a malfunction catalyst diagnostic tests in a power train

A method for controlling a malfunction catalyst diagnostic tests in a drive train comprising an internal combustion engine and a post-treatment system including a device for selective catalytic reduction, wherein said assay detects a malfunction state of a catalyst in the apparatus for selective catalytic reduction, the method comprising: Monitoring an exhaust gas stream in the post-treatment system; Estimating an effect of the exhaust stream to an estimated reducing agent stored on a catalyst in the apparatus for selective catalytic reduction; and selectively deactivating the catalyst malfunction diagnostic tests based on the estimation of the effect of the exhaust stream to the estimated reducing agent storage; marked by Determining a reducing agent storage that is required for the efficient operation of the device for selective catalytic reduction; wherein the step of selectively deactivating the catalyst malfunction diagnostic test is performed when the estimated reductant storage is less than the reducing agent storage that is required for the efficient operation of the device for selective catalytic reduction.