Method for controlling an energy recovery system of an exhaust line of a motor vehicle engine, this energy recovery system comprising: - a bypass duct, pierced at both ends thereof (31A, 31B), into an exhaust duct of said exhaust line of the engine and comprising a heat exchanger, and - a bypass valve arranged in said exhaust duct, at the inlet of said bypass duct, said bypass valve being designed to assume different positions in said exhaust duct, - said control method comprising the following steps: a) determining, at the moment t, values of the injected fuel flow rate Q fuel (t) into said engine, of the inlet air flow rate Q air (t) into said engine, of the temperature of the exhaust gases Texh(t), and of the flow of the exhaust gases Q exh (t) circulating in said exhaust duct; b) determining, at the moment t, an optimum position of said bypass valve on the basis of: - a fuel consumption saving S recov provided thanks to the energy recovery system, corresponding to the values of the temperature of the exhaust gases Texh(t) and of the flow of the exhaust gases Q exh (t) determined in step a), and - an overconsumption of fuel O consu associated with the implementation of the energy recovery system for said optimum position of the bypass valve, corresponding to the values of the injected fuel flow rate Q fuel(t), of the inlet air flow rate Q air (t), and of the temperature of the exhaust gases Texh(t) determined in step a) and to the optimum position of the bypass valve; c) positioning said bypass valve in said optimum position determined in step b). - a bypass duct, pierced at both ends thereof (31A, 31B), into an exhaust duct of said exhaust line of the engine and comprising a heat exchanger, and - a bypass valve arranged in said exhaust duct, at the inlet of said bypass duct, said bypass valve being designed to assume different positions in said exhaust duct, - said control method comprising the following steps: a) determining, at the moment t, values of the injected fuel flow rate Q fuel (t) into said engine, of the inlet air flow rate Q air (t) into said engine, of the temperature of the exhaust gases Texh(t), and of the flow of the exhaust gases Q exh (t) circulating in said exhaust duct; b) determining, at the moment t, an optimum position of said bypass valve on the basis of: - a fuel consumption saving S recov provided thanks to the energy recovery system, corresponding to the values of the temperature of the exhaust gases Texh(t) and of the flow of the exhaust gases Q exh (t) determined in step a), and - an overconsumption of fuel O consu associated with the implementation of the energy recovery system for said optimum position of the bypass valve, corresponding to the values of the injected fuel flow rate Q fuel(t), of the inlet air flow rate Q air (t), and of the temperature of the exhaust gases Texh(t) determined in step a) and to the optimum position of the bypass valve; c) positioning said bypass valve in said optimum position determined in step b). a) determining, at the moment t, values of the injected fuel flow rate Q fuel (t) into said engine, of the inlet air flow rate Q air (t) into said engine, of the temperature of the exhaust gases Texh(t), and of the flow of the exhaust gases Q exh (t) circulating in said exhaust duct; b) determining, at the moment t, an optimum position of said bypass valve on the basis of: - a fuel consumption saving S recov provided thanks to the energy recovery system, corresponding to the values of the temperature of the exhaust gases Texh(t) and of the flow of the exhaust gases Q exh (t) determined in step a), and - an overconsumption of fuel O consu associated with the implementation of the energy recovery system for said optimum position of the bypass valve, corresponding to the values of the injected fuel flow rate Q fuel(t), of the inlet air flow rate Q air (t), and of the temperature of the exhaust gases Texh(t) determined in step a) and to the optimum position of the bypass valve; - a fuel consumption saving S recov provided thanks to the energy recovery system, corresponding to the values of the temperature of the exhaust gases Texh(t) and of the flow of the exhaust gases Q exh (t) determined in step a), and - an overconsumption of fuel O consu associated with the implementation of the energy recovery system for said optimum position of the bypass valve, corresponding to the values of the injected fuel flow rate Q fuel(t), of the inlet air flow rate Q air (t), and of the temperature of the exhaust gases Texh(t) determined in step a) and to the optimum position of the bypass valve; c) positioning said bypass valve in said optimum position determined in step b).