A method for adjusting an exhaust gas recycling rate in an internal combustion engine exhaust gas recycling system, comprising: arranging the exhaust gas recycling system in at least one of a fresh gas line, an exhaust gas line, and an exhaust gas recycling line of the internal combustion engine; actuating at least one additional valve; adjusting the at least one additional valve temporarily by changing the operation of the internal combustion engine based on an exhaust gas rate associated with a current operating point of the internal combustion engine; diagnosing the at least one additional valve; and evaluating the change of at least one engine operating parameter dependent on the exhaust gas recycling rate.