Higher Tool Confidence Level (TCL) is needed for tools used on the verification of safety-critical SoCs, aiming to achieve the required Automotive Safety Integrity Level in ISO 26262. This paper presents a methodology to improve the confidence level of functional safety verification flow. To do this, we compare the fault-list generated by the fault injection (FI) simulator with the Automatic Test Pattern Generation (ATPG) flow for stuck-at (SA) fault types. Moreover, we compare fault coverage results by using test vectors generated by the ATPG tool so the result of the FI simulation is compared to the results gained from the ATPG. This is a way to improve simulator’s confidence level by taking advantage of strength of the ATPG.