A diagnostic system and a diagnostic method for a technical system are described with which, on the basis of the expert knowledge already necessary for the manual establishment of troubleshooting trees, the establishment of troubleshooting trees can be automated and the performance of guided troubleshooting can be assisted. Provided for this purpose are an acquisition module for systematic acquisition of all relevant status, observation, and/or measured data of the technical system, and a prioritization module for prioritizing all relevant tests, checks, or measurements, in order, in accordance with the weightings of the tests, checks, or measurements as a function of the status, observation, and/or measured data, to establish automatically a troubleshooting tree that can serve as a basis for guided troubleshooting.