Method for detecting a presence or absence of a leak in a fuel system

It is proposed a method for detecting a presence of a leak in a fuel system mounted on board of a vehicle. The method is such that it comprises the steps of: a) obtaining (S1,S6) temperatures and pressures in the fuel system at a first time and at a second later time; b) calculating (S8) a pressure expected in the fuel system at the second time, on the basis of at least one of the temperatures and pressures obtained at the first and second times, and a coefficient that represents the natural evolution of pressure in the fuel system over time; c) detecting (S9) a leak by comparing the calculated expected pressure and the pressure obtained at the second time to at least one predetermined threshold.