This paper describes the development and the validation of two complete vehicle models, achieved within the LMS Imagine.Lab AMESim platform and aiming to help in the understanding of the contributions of different sub-systems to CO2 emissions. The models that include the main components of the vehicle (powertrain, coolant and oil circuits, electrical system) take into account the physical interactions and enable both to predict fuel consumption and to develop and validate control strategies for the mild hybrid part. Some measurements have been performed on European driving cycle and allow correlating fuel and electrical consumptions.