defects and parameter variations often cause design timing failures. It is essential that those errors be correctly and quickly diagnosed. The existing delay-fault diagnosis algorithms cannot identify the delay faults that require nonrobust tests, because they ignore non-robust propagation conditions while emulating the failure analyzer?s behavior. We propose a novel approach to perform delay-fault diagnosis for robust and non-robust tests. The experimental results show that our approach can diagnose delay faults with good resolution. It is stable with respect to delay variations that the failure analyzer might experience.