A method for operating a driving system of a motor vehicle, in particular, the driving system having an internal combustion engine and at least one electric motor, and during warm-up of the internal combustion engine, the latter being loaded with a specifiable torque; and the at least one electric motor generating a torque at least at times, to unload or load the internal combustion engine. An actual torque of the internal combustion engine is compared to a specifiable first setpoint torque of the internal combustion engine; a difference of the actual torque from the first setpoint torque being formed; and a time integral being formed over the difference formed; and a fault being detected in the warm-up of the internal combustion engine, as a function of the time integral formed.