A route-oriented self-diagnosis method for the technical state of modules and connection lines of digital systems is designed. It uses 0-routes for choosing testing modules and transferring test results. Self-diagnosis is subdivided into two stages: determination of a reliably operative module for starting self-diagnosis and self-diagnosis of the state of other components of the system. Test results for modules are described with the Preparat-Metze-Chien model. Two examples on self-diagnosis of failed components in a 9-module system are given.