Method and device for the dynamic monitoring of a lambda probe

A method for the dynamic monitoring of a first lambda probe arranged in an exhaust-gas duct of an internal combustion engine upstream of an exhaust-gas purification system. A period of an output signal of the first lambda probe is determined in a controller of the internal combustion engine, and a lambda regulating signal is determined from an output signal of a second lambda probe connected downstream of the exhaust-gas purification system. A first threshold value for a lengthening of the period of the output signal of the first lambda probe is predefined, in that a characteristic signal (46) is derived from the lambda regulating signal, in that a second threshold value for an inadmissible deviation of the characteristic signal (46) is predefined, and in that an inadmissible asymmetric delay of the first lambda probe is inferred if the lengthening of the period exceeds the first threshold value and the characteristic signal (46) deviates from the second threshold value outside predetermined limits.