A method for operating a hybrid drive device of a motor vehicle that has at least two different drive aggregates, in particular an electric motor and an internal combustion engine, and having a clutch, the drive aggregates being capable of being operatively connected using the clutch. It is provided that, in a diagnostic and/or adaptation operating mode; the clutch is operated with a slippage. In addition, the present system relates to a hybrid drive device, a control device for a hybrid drive device, and a motor vehicle aggregate that has both the control device and the hybrid drive device.