In a method and device for controlling and/or monitoring the function of a secondary air supply in an emission control system of an internal combustion engine, the emission control system includes at least two catalytic converters situated in succession in an exhaust duct, it being possible for the second catalytic converter to be implemented as a combination of catalytic converter and particulate filter. For a secondary air diagnosis and for secondary air control, a two-point lambda probe is situated, with respect to a direction of flow of exhaust gas, downstream of the first catalytic converter. Measures are applied for compensating tolerance and aging effects of the two-point lambda probe. This results in particular in cost advantages in emission control systems for fulfilling stricter emission requirements. In particular, this makes it possible to operate the particulate filter in optimized fashion.