A method to control an internal combustion engine (1) having an exhaust duct (10) and an exhaust gas after-treatment system (14) comprising at least one catalytic converter (15, 17) arranged along the exhaust duct (10); an oxygen sensor (18, 18*) housed along the exhaust duct (10) and arranged upstream of said at least one catalytic converter (15, 17); and a burner (21) suited to introduce the exhaust gases into the exhaust duct (10) upstream of the oxygen sensor (18, 18*) the method provides the steps of identifying the operation phases in which the internal combustion engine (1) is turned off and the burner (21) is turned on so that the oxygen sensor (18, 18*) is exclusively hit by the exhaust gases produced by the burner (21); acquiring the signal generated by the oxygen sensor (18, 18 * ); and using the signal generated by the oxygen sensor (18, 18*) to determine the objective fuel flow rate (ṁ F_OBJ ) and the objective air flow rate (ṁ A_OBJ ) to be fed to the burner (21) .