A great part of the projects in the powertrain area is focused on the development of more efficient thermal applications. In the end, efficiency is pursued, since the aim is to achieve a sustainable design with low fuel consumption. Thus, vehicles which present lower fuel consumption are demanded by customers. Additionally the emission standards have been reducing the limits of CO₂ emissions to very low levels, which drive engineers to develop vehicles with lower fuel consumption. In summary, the product should now please a more demanding worldwide customer profile as the global economy grows. Vehicle design processes should consider fuel consumption sensitivity taking into account the combined engine and drive train systems at early stages. Frequently the actual fuel consumption can only be confirmed when the first prototype is assembled in order to validate the adopted solutions. On the other hand, project timing is another dominant constraint, even when using planning of experiments (DoE) not all proposed designs can be tested. In this sense, the use of numerical simulation resources has been more and more utilized to reduce project timing. A vehicle simulation of a 4-cylinder diesel internal combustion engine (ICE) coupled with the driveline of the vehicle, including its accessories, was developed utilizing the numerical 1D model, built in GT-Suite, a Gamma Technologies, Inc., code. A multi-body dynamics method was used with explicit consideration of accessory loads and the engine, which was represented by its maps evaluated at the dyno, namely BMEP, FMEP and BSFC. The model calibration was done using some route acquired data in order to reproduce the measured fuel consumption under some specific vehicle cruise conditions and 3 accelerations ramp situations. The pedal position was assigned by a PID controller representing a virtual driver's behavior. The gear shift schedule was calculated inversely by inspection pursuing a reasonable correlation of the simulated and measured fuel rates. The aerodynamics features and the rolling resistance coefficient were adopted based on information provided by the customer and the dynamic tire radius were inversely calculated using GPS vehicle speed data, engine speed and drive line ratios.This paper presents a study of the impact of accessory loads in a physically-representative way. Their loads have been considered via their power consumption curve. Each one has been studied and modeled in order to get a representative power curve shape over the relevant speed range for the engine. Then, they were all included in the 1D dynamic model. The final numerical model presented 6% of max difference in total fuel consumption in comparison to measurements for all 6 cruise situations without the need of any calibration adjustment, which is a usual practice worldwide. The acceleration behavior of the model presented a max difference of 7% (with a minimum of 2%) in comparison to measurements in terms of acceleration times and vehicle displacements. The aforementioned results were considered excellent from the perspective of the adopted 1D approach. The model has already served as a good basis to evaluate the contribution of each accessory load on the total fuel consumption in order to provide technical basis for a system optimization, which might lead to an eventual modification of the accessory design. Last but not least, it may help with the accessory supplier competition.