An efficient automotive simulation method for intentional electromagnetic interference (IEMI) is developed. As the full automotive simulation is computationally demanding, running the simulation for all possible IEMI attack locations is prohibitive. Therefore, a new methodology based on the reciprocity theorem is proposed to replace all regular simulations by one special simulation. The special simulation uses the reverse model which is defined by switching the location of source and observation point in the regular automotive simulation model. The reciprocity based simulation is validated by comparing the simulated results with all measured data in the IEMI experiment.