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 (28, 30) close to the engine and a second SCR catalytic converter downstream of the first SCR catalytic converter (28, 30) are arranged in the flow direction of an exhaust gas of the internal combustion engine, wherein upstream of the first SCR catalytic converter (28, 30) 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 (28, 30), and downstream of the first SCR catalytic converter (28, 30) 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 (28, 30) 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 (28, 30, 32) is modeled and measured, before and after the SCR catalytic converters (28, 30, 32), by nitrogen oxide sensors (54, 56, 58) while the ammonia fill level on the first SCR catalytic converter (28, 30) 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 (28, 30) 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 (28, 30, 32) is modeled and measured, before and after the SCR catalytic converters (28, 30, 32), by nitrogen oxide sensors (54, 56, 58) while the ammonia fill level on the first SCR catalytic converter (28, 30) 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.