Method for updating a function for calculating the exhaust pressure of an internal combustion engine

A method of updating a pressure law (P-LAW) providing the exhaust pressure (P) as a function of the exhaust gas flow rate (Q); the following steps are included: measuring a first current intensity (Ip) of a UEGO sensor (13), under conditions of pure air and at a reference exhaust pressure (P); measuring a second current intensity (Ip) of the UEGO sensor (13) under conditions of pure air and at a different exhaust pressure (P); estimating the exhaust gas flow rate (Q) at the moment of measuring the second current intensity (Ip); determining a current difference (ΔIp); determining an exhaust pressure (P) corresponding to the current difference (ΔIp) by using a constructional feature (C-LAW) of the UEGO sensor (13); and using the exhaust gas flow rate (Q) corresponding to the current difference (ΔIp) and the exhaust gas flow rate (Q) at the moment of measuring the second current intensity (Ip) in order to update the pressure law (P-LAW).