The effects of permanent faults, arising along working life of digital electronic systems, may impact their reliability and performance. In-field test may help to detect these faults and to prevent serious effects in safety-critical applications. Distributed electronic systems introduce further complexity in this scenario, as the low observability and the lack of maintenance make difficult the detection as well as the identification of failing elements and their repairing. Functional workloads are often used for on-line tests of distributed systems to detect permanent faults. Suitable techniques for test generation and early identification of functionally untestable permanent faults are critical issues that are faced in this work.