Method for operating an exhaust gas aftertreatment system of an internal combustion engine , wherein the internal combustion engine is connected by its outlet to an exhaust gas system in which a first SCR catalytic converter close to the engine and a second SCR catalytic converter downstream of the first SCR catalytic converter are arranged in the flow direction of an exhaust gas of the internal combustion engine , wherein upstream of the first SCR catalytic converter a first metering element is arranged, by means of which a reducing agent can be metered into the exhaust gas duct upstream of the first SCR catalytic converter , and downstream of the first SCR catalytic converter and upstream of the second SCR catalytic converter a second metering element for metering in the reducing agent is arranged, which method comprises the following steps: - determining a component temperature (T SCR2 ) of the second SCR catalytic converter and/or an exhaust gas temperature (T EG ) at the second SCR catalytic converter ; - comparing the determined component temperature (T SCR2 ) or the determined exhaust gas temperature (T EG ) with a relevant threshold temperature (T S1 , T S2 ); - determining an ammonia fill level of the second SCR catalytic converter ; - lowering the ammonia fill level of the first SCR catalytic converter if the second SCR catalytic converter exceeds a critical fill level and the component temperature (T SCR2 ) or the exhaust gas temperature (T EG ) is above the relevant threshold value (T S1 , T S2 ); - converting the nitrogen oxides in the exhaust gas stream of the internal combustion engine by means of the second SCR catalytic converter , the ammonia fill level of the second SCR catalytic converter thereby being reduced, wherein - an efficiency of the SCR catalytic converters is modeled and measured, before and after the SCR catalytic converters , by nitrogen oxide sensors while the ammonia fill level on the first SCR catalytic converter is being lowered, wherein - if the efficiency falls below a defined threshold value, the metering in of the reducing agent by the second metering element is switched from a fill level control to a pre-controlled metering. - determining a component temperature (T SCR2 ) of the second SCR catalytic converter and/or an exhaust gas temperature (T EG ) at the second SCR catalytic converter ; - comparing the determined component temperature (T SCR2 ) or the determined exhaust gas temperature (T EG ) with a relevant threshold temperature (T S1 , T S2 ); - determining an ammonia fill level of the second SCR catalytic converter ; - lowering the ammonia fill level of the first SCR catalytic converter if the second SCR catalytic converter exceeds a critical fill level and the component temperature (T SCR2 ) or the exhaust gas temperature (T EG ) is above the relevant threshold value (T S1 , T S2 ); - converting the nitrogen oxides in the exhaust gas stream of the internal combustion engine by means of the second SCR catalytic converter , the ammonia fill level of the second SCR catalytic converter thereby being reduced, wherein - an efficiency of the SCR catalytic converters is modeled and measured, before and after the SCR catalytic converters , by nitrogen oxide sensors while the ammonia fill level on the first SCR catalytic converter is being lowered, wherein - if the efficiency falls below a defined threshold value, the metering in of the reducing agent by the second metering element is switched from a fill level control to a pre-controlled metering. <EOS>