A condition monitoring activity consists in the analysis of several information from the engine and the subsequent data elaboration to assess its operating condition. By means of a continuous supervision of the operating conditions the internal combustion engine performance can be maintained at design-level in the long term.The growing use of turbocharger (TC) in automotive field suggests to use the TC speed as a possible feedback of engine operating condition. Indeed, the turbocharger behavior is influenced by the thermo and fluid-dynamic conditions in the cylinder exhaust port: this feature suggests that the TC speed could provide useful data about the engine cycle.In this study the authors describe a theoretical and numerical analysis focused on the TC speed in a four stroke turbo-diesel engine. The purpose of this study is to highlight whether the TC speed allows one to detect the variation of the engine parameters. In addition, when the TC speed alone is not sufficient to detect the variation in the engine operating conditions, the proper set of additional, easy-to-measure, engine parameters is studied to univocally identify the causes of the variation. The analysis was carried out numerically by using a commercial 1D code calibrated with experimental data on a four cylinders diesel engine coupled with a turbocharger.The numerical data was analyzed to estimate the optimal set of information required to identify the changed engine parameter that affects in particular the combustion process. By using the calibrated model, a sensitivity analysis of the detection parameter response, with particular attention to TC speed variations, was carried out by varying the operating conditions of the engine such as fuel mass flow rate, EGR rate and back pressure at the turbine outlet.