Functional test methodologies such as Software-Based Self-Test appear to suit well SoC delay fault testing. State-of-the-art solutions in this topic are quite far from maturity and few works consider Software-based Diagnosis for delay faults. In this paper we evaluate benefits and costs in using symbolic simulation for SoCs, in particular focusing on embedded processor core testing. Symbolic simulation principles are key to enable fast analysis and speed up delay fault diagnosis; to cope with SoC behavior, the traditional 6-valued symbolic algebra was expanded in order to tackle X and Z logic states. As a case study we consider a large design including many core types and suitable DFT for performing high quality test without scan chains.