Method for operating a drive device and corresponding drive device

A drive device, comprising:

• a drive unit producing exhaust gas and an exhaust gas posttreatment device designed as a vehicle catalytic converter for posttreatment of the exhaust gas, wherein the drive device is provided and designed to measure a first measured value describing the residual oxygen content in the exhaust gas by a first lambda sensor arranged upstream of the exhaust gas posttreatment device and to measure a second measured value describing the residual oxygen content in the exhaust gas by a second lambda sensor arranged downstream of the exhaust gas posttreatment device, wherein the combustion air ratio of a fuel-air mixture used to operate the drive unit is set during an at least temporarily performed normal operating mode on the basis of the first measured value, the second measured value, and the threshold value for the second measured value, wherein the drive device is furthermore provided and designed to ascertain the threshold value in that during an at least temporarily performed calibration operating mode, the combustion air ratio is periodically changed over time around a variable mean value at a determined amplitude and a determined frequency and the threshold value is ascertained from the second measured value when a variation of the second measured value over time caused by the change of the combustion air ratio falls below a variation threshold value.