A method is provided for checking the functional capacity of a liquid-cooled exhaust manifold of an internal combustion engine, having an exhaust line connected to the exhaust manifold, in the course of which an exhaust gas sensor having an electrical heater is arranged. During the operation of the internal combustion engine, the electrical resistance of the exhaust gas sensor is determined, on the basis of which the current value of the exhaust gas temperature is evaluated, and compared to a target value of the exhaust gas temperature, which is expected at this point in the operation of the internal combustion engine. Depending on the result of the comparison, the functional capacity of the liquid-cooling of the exhaust manifold is estimated.