An object of the present invention is to restrain a deterioration of emission even if the actual control condition including the required torque is different from the set control condition. Such silicon precursor compositions comprise at least a silane or disilane derivative that is substituted with at least one alkylhydrazine functional groups and is free of halogen substitutes. In particular, the method uses wavelet analysis to encode essential information in time-frequency transformations and provides a signal model for an operating fault or normal operation of a system of interest.