To better reflect real world driving conditions, the EPA 5-Cycle Fuel Economy method encompasses high vehicle speeds, aggressive vehicle accelerations, climate control system use and cold temperature conditions in addition to the previously used standard City and Highway drive cycles in the estimation of vehicle fuel economy.A standard Powersplit Hybrid Electric Vehicle (HEV) system simulation environment has long been established and widely used within Ford to project fuel economy for the standard EPA City and Highway cycles. Direct modeling and simulation of the complete 5-Cycle fuel economy test set for HEV's presents significant new challenges especially with respect to modeling vehicle thermal management system and interactions with HEV features and system controls. It also requires a structured, systematic approach to validate the key elements of the system models and complete vehicle system simulations.This paper describes a methodology developed at Ford for system simulation and analysis of EPA 5-Cycle fuel economy for powersplit HEV's. Important newly developed elements of the vehicle system models are explained including the modeling of vehicle and engine controls and the procedures of running simulations in accordance with 5-Cycle fuel economy test procedures. Examples of using the system simulation for control calibration optimization to balance 5-Cycle FE and other vehicle attributes are presented. Finally, the paper describes a process for verifying and maintaining the accuracy of the HEV system models over the course of a production vehicle program.