Method for operating an internal combustion engine with a secondary air system

A method is disclosed for operating an internal combustion engine which comprises a primary air system for providing fresh air and a secondary air system. The secondary air system is configured to branch off secondary air from the primary air system and blow it into an exhaust gas duct. The secondary air system has a compressor for feeding the secondary air and a secondary air valve for shutting off or enabling the blowing in of secondary air. The method includes (i) activating the compressor while the secondary air valve is kept closed, (ii) determining whether compressor surging is occurring or is directly imminent, (iii) sensing at least one sensor signal if compressor surging is occurring or is directly imminent, and (iv) determining whether there is a leak in the secondary air system, on the basis of the sensed sensor signal.