Diagnostics method and system for a power plant having two staged turbocompressors

A diagnostic system for a power train including at least one low-pressure turbocharger and at least one high-pressure turbocharger, the high-pressure turbocharger including a high-pressure turbine and a high-pressure compressor, the turbochargers being staged, and supplying an internal combustion engine, the power train being installed in an engine vehicle, the diagnostic system comprising:

• means for determining a mode of operation of the power train as a function of a position of a high-pressure bypass and of pressure upstream of the high-pressure turbine, the high-pressure bypass being connected between an inlet and an outlet of the high-pressure turbine
• a first means for estimating power of the high-pressure turbine, the first means being linked to an output of the means for determining the mode of operation of the power train;
• a second means for estimating the power of the high-pressure turbine;
• and
• means for estimating a failure criterion connected at an input to the first means for estimating the power of the high-pressure turbine and to the second means for estimating the power of the high-pressure turbine and at an output to a comparison means configured to compare the failure criterion to stored values.