Method for estimating the instantaneous exhaust pressure of a vehicle engine, the engine being connected to an exhaust manifold, the vehicle comprising at least one camshaft controlling inlet and exhaust valves, characterised in that the method comprises the steps of: - determining an engine speed and a total gas filling at the exhaust; - calculation of intermediate pressure ratios from mappings with as their input the engine speed and the total filling, the intermediate pressure ratios established at the output of the mappings being the pressure ratios for predetermined positions of the inlet or exhaust valves; - calculation of a global pressure ratio by interpolation of the intermediate pressure ratios; and - multiplication of the global pressure ratio by a reference exhaust pressure, the product of the multiplication determining the instantaneous exhaust pressure, the total filling D being given by the formula: D = k 1 × debit ρ 0 × V 0 × N × Nbr_cyl × T 0 T ech × P 0 P atmo with: debit (flowrate) = flowrate ex for a naturally aspirated engine or one capable of being supercharged, or debit (flowrate) = flowrate turbine = flowrate ex - flowrate wastegate, the engine being supercharged; and with: flowrate ex: total exhaust flowrate in [kg/s]: flowrate ex = flowrate fresh_air + flowrate swept_air + flowrate petrol − flowrate EGR + flowrate IAE flowrate fresh_air: flowrate of fresh air issuing from the filling with fresh air in [kg/s], flowrate swept_air: flowrate of fresh air swept from the inlet to the exhaust in [kg/s], flowrate petrol: flowrate of petrol injected in [kg/s], flowrate EGR: EGR flowrate in [kg/s], flowrate IAE: IAE flowrate in [kg/s] flowrate turbine: total flowrate passing through the turbine in [kg/s], flowrate wastegate: flowrate of air passing through the wastegate in [kg/s], Nbr_cy /: number of cylinders of combustion engine, ρ 0: standardisation density in [kg/m 3], V 0: standardisation volume: unit cubic capacity of the engine in, T ex: exhaust temperature in the manifold in, T 0: standardisation temperature in, P 0: standardisation pressure in [Pa], P atmo: atmospheric pressure in [Pa], N: engine speed in [rev/min], k 1: unit conversion coefficient. - determining an engine speed and a total gas filling at the exhaust; - calculation of intermediate pressure ratios from mappings with as their input the engine speed and the total filling, the intermediate pressure ratios established at the output of the mappings being the pressure ratios for predetermined positions of the inlet or exhaust valves; - calculation of a global pressure ratio by interpolation of the intermediate pressure ratios; and - multiplication of the global pressure ratio by a reference exhaust pressure, the product of the multiplication determining the instantaneous exhaust pressure, flowrate ex: total exhaust flowrate in [kg/s]: flowrate fresh_air: flowrate of fresh air issuing from the filling with fresh air in [kg/s], flowrate swept_air: flowrate of fresh air swept from the inlet to the exhaust in [kg/s], flowrate petrol: flowrate of petrol injected in [kg/s], flowrate EGR: EGR flowrate in [kg/s], flowrate IAE: IAE flowrate in [kg/s] flowrate turbine: total flowrate passing through the turbine in [kg/s], flowrate wastegate: flowrate of air passing through the wastegate in [kg/s], Nbr_cy /: number of cylinders of combustion engine, ρ 0: standardisation density in [kg/m 3], V 0: standardisation volume: unit cubic capacity of the engine in, T ex: exhaust temperature in the manifold in, T 0: standardisation temperature in, P 0: standardisation pressure in [Pa], P atmo: atmospheric pressure in [Pa], N: engine speed in [rev/min], k 1: unit conversion coefficient.