Abstract: A measurement method is provided for an SCR exhaust gas aftertreatment system of a vehicle, where the SCR exhaust gas aftertreatment system includes a first NOx sensor, which is arranged in the exhaust gas flow upstream of the SCR catalytic converter and the urea introducing device; and a second NOx sensor, which is arranged in the SCR catalytic converter or in the exhaust gas flow downstream of the SCR catalytic converter. According to the method, a first signal is determined by the first NOx sensor. This first signal can also be a time delayed signal. In addition, a second signal is determined by a second NOx sensor. Based on the first and the second signal, a linearity indication, such as correlation coefficient, is determined that is a measure for the linear correlation between both signals. The linearity indication can be used to differentiate between an NOx slip and an NH3 slip.