A method for the on-board diagnosis of a control unit which include a hypervisor and at least one guest system operated under the hypervisor. In the method, the guest system receives a diagnosis inquiry at an individual diagnosis address of the guest system from a diagnostic tool with the aid of a communication infrastructure. The guest system makes a self-diagnosis. The guest system receives a hypervisor diagnosis from the hypervisor. The guest system transmits, at its diagnosis address, the self-diagnosis or the hypervisor diagnosis to the diagnostic tool as a function of the diagnosis inquiry.