The invention relates to a method of ensuring the safety of the components of the drive train of a vehicle equipped with a heat engine, before or during its startup phase following a deterioration of the quality of the fuel contained in the tank (2) and the fuel feed system of the engine, said method comprising a step of diagnosing the type and extent of the deterioration of the quality of the fuel, said step being based on the measurement of the interactions between an electronmagnetic radiation and the constituent molecules of the fuel, said measurement being performed by a system of analysis, and a step of activating a system (13) to ensure the safety of the components of the drive train as a function of the results of the analysis step.