Electromagnetic Interference contributes to a significant percentage of failures in the verification stage of automotive electronics design cycle. Today these issues are caught late in the design cycle leading to delay in time-to-market. An effective simulation methodology is key to catching the problems at an early design stage. However, accurate system-level analysis is time intensive. This letter presents a model-based simulation methodology for system-level immunity characterization at an early design stage. The simulation framework is comprised of a hybrid 2D-3D electromagnetic solver and a circuit solver. IC immunity model (ICIM) is inducted into the simulation environment to accurately predict the immunity behavior in a Bulk Current Injection (BCI) test. The proposed method is validated by comparing the simulation prediction with the actual BCI measurement. Further, layout changes are made based on simulation to mitigate the measurement failure. This emphasizes the use of model-based simulation to predict immunity performance at early product design cycle.