The work that we present in this paper contributes to the field of supervision, monitoringand control of complex discrete event systems services. It is placed in the context of randomfailure occurrence of operative parts where we focus on providing tools to maintenance teamsby locating the possible origin of potential defect products: better locate to better maintain, soeffectively to minimize more equipment’s time drift. If the production equipment were able todetect such drifts, the problem could be considered simple; however, metrology equipment addsto the complexity. In addition, because of an impossibility to equip the production equipment witha sensor system which comprehensively covers all parameters to be observed, a variable sensorreliability in time and a stressed production environments, we propose a probabilistic approachbased on Bayesian network to estimate real time confidence, which can be used for productionequipment?s operation.