Method of operating an aftertreatment system of an automotive system

Said aftertreatment system comprise a Diesel Particulate Filter (DPF, 500, figure 3), and the DPF is equipped with a brick (530, figure 3). Said method comprises the steps of: performing a DPF regeneration 700; obtaining pressure values upstream and downstream of the DPF; calculating a difference Δp of pressure between the pressure values upstreamand downstream of the DPF, 730; reading from a map, a value representative of a backpressure 735 due to the brick of the DPF; calculating a ratio between the pressure difference and the brick backpressure 740, using the calculated ratio to correct the output of the map (535, figure 3). The invention can also comprise an apparatus which has means for performing the steps of the method above. The method allows for an automatic correction of the values of the clean map and can reduce the calibration time needed for calibrating a clean map. The method can also vary the length of the DPF regeneration by a first predetermined percentage before obtaining the pressure values 720. It can also vary the length of the regeneration by a second predetermined percentage before obtaining the pressure values depending on if efficient DPF regeneration conditions are met 725.