Diagnostics method for a supercharged internal combustion engine equipped with a fixed-geometry turbocharger comprising a compressor through which the air admitted to the intake circuit of the engine passes, and a turbine rotationally connected to the compressor by a common shaft and through which exhaust gases from the engine pass in the exhaust circuit of the engine, said engine being associated with: - a throttle valve for varying the bore section for the air admitted to the intake circuit of the engine; and - a wastegate valve mounted in parallel with the turbine in the exhaust circuit of the engine in order to vary the proportion of exhaust gases from the engine passing through the turbine, CHARACTERIZED IN THAT it comprises: - a step of calculating a first integral with respect to time (I 1) of a measurement of the atmospheric pressure (P atm) during a calculation time; - a step of calculating an integral with respect to time (I 2) of a measurement of the boost pressure (P boost) during said calculation time; - a step of calculating a second integral with respect to time (I 3) of a measurement of the atmospheric pressure (P atm) during said calculation time; - a step of calculating two diagnostics criteria (C 1, C 2) dependent on the first integral with respect to time (I 1) of the atmospheric pressure (P atm), on the integral with respect to time (I 2) of the boost pressure (P boost) and on the second integral with respect to time of the atmospheric pressure (P atm); - a step of comparing the first diagnostics criterion (C 1) with a first diagnostics threshold (S 1) and of comparing the second diagnostics criterion (C 2) with a second diagnostics threshold; and - a step of diagnosing a fault when one of the two diagnostics criteria (C 1, C 2) at least is below its associated diagnostics threshold (S 1, S 2). - a throttle valve for varying the bore section for the air admitted to the intake circuit of the engine; and - a wastegate valve mounted in parallel with the turbine in the exhaust circuit of the engine in order to vary the proportion of exhaust gases from the engine passing through the turbine, - a step of calculating a first integral with respect to time (I 1) of a measurement of the atmospheric pressure (P atm) during a calculation time; - a step of calculating an integral with respect to time (I 2) of a measurement of the boost pressure (P boost) during said calculation time; - a step of calculating a second integral with respect to time (I 3) of a measurement of the atmospheric pressure (P atm) during said calculation time; - a step of calculating two diagnostics criteria (C 1, C 2) dependent on the first integral with respect to time (I 1) of the atmospheric pressure (P atm), on the integral with respect to time (I 2) of the boost pressure (P boost) and on the second integral with respect to time of the atmospheric pressure (P atm); - a step of comparing the first diagnostics criterion (C 1) with a first diagnostics threshold (S 1) and of comparing the second diagnostics criterion (C 2) with a second diagnostics threshold; and - a step of diagnosing a fault when one of the two diagnostics criteria (C 1, C 2) at least is below its associated diagnostics threshold (S 1, S 2).