Matrix method for diagnosing functional failures and stuck-at faults in software or hardware units is proposed. It is based on qubit or multi-valued data structures for defining diagnostic information, which allows significantly reducing the computational complexity of the simulation and diagnosis due to the introduction of parallel logical operations on the matrix data. The qubit method for fault-free simulating digital units with the possibility of online repair of digital system components is presented. It is characterized by significantly improved performance due to addressed processing procedure of the functional primitives, defined by qubit vectors of output states.