Method for adapting the signal (λ) measured by a lambda probe for detecting the concentration of oxygen operating in an exhaust line of an internal combustion engine of a vehicle, of the type comprising acquiring (35, 33) in processing means, in particular in an engine control unit, said measured signal (λ) and performing a correction of values (Om) obtained from said signal (λ) measured by said lambda probe in an operating condition of the engine in which there are exhaust gases in said exhaust line through the phases of: obtaining adaptation values (Ot) from the signal (λ) measured by said lambda probe in a determined engine operating phase wherein in said exhaust line there are no exhaust gases, and comparing said adaptation values (Ot) of the measured signal (λ) with expected values (Or) for a reference oxygen concentration, calculating an adaptation factor (Fc) as a function of said adaptation values (Ot) and expected values (Or) to be used in said operation for correcting values (Or) obtained from said signal (λ) measured by said lambda probe in an operating condition of the engine in which there are exhaust gases, characterised in that said operation for obtaining adaptation values (Ot) from the signal (λ) measured by said lambda probe in a determined engine operating phase wherein in said exhaust line there are no exhaust gases is carried out in a phase for shutting off the engine in which the engine is performing rotations and wherein the injection (21, 22) of fuel is at zero, and in that said method comprises, during said phase of shutting off the engine, reaching a stand-by operating state comprising keeping said lambda probe active and operative, in said stand-by state being performed the measurement of a number of rotations (Nr) of the engine occurring in absence of injection and comparing said number of rotations with a threshold value (Nrt) indicating the presence of air alone in the exhaust line to pass to an active state in which there is carried out said operation for obtaining adaptation values (Ot) from the signal (λ) measured by said lambda probe in a determined engine operating phase wherein in said exhaust line there are no exhaust gases. obtaining adaptation values (Ot) from the signal (λ) measured by said lambda probe in a determined engine operating phase wherein in said exhaust line there are no exhaust gases, and comparing said adaptation values (Ot) of the measured signal (λ) with expected values (Or) for a reference oxygen concentration, calculating an adaptation factor (Fc) as a function of said adaptation values (Ot) and expected values (Or) to be used in said operation for correcting values (Or) obtained from said signal (λ) measured by said lambda probe in an operating condition of the engine in which there are exhaust gases, characterised in that said operation for obtaining adaptation values (Ot) from the signal (λ) measured by said lambda probe in a determined engine operating phase wherein in said exhaust line there are no exhaust gases is carried out in a phase for shutting off the engine in which the engine is performing rotations and wherein the injection (21, 22) of fuel is at zero, and in that said method comprises, during said phase of shutting off the engine, reaching a stand-by operating state comprising keeping said lambda probe active and operative, in said stand-by state being performed the measurement of a number of rotations (Nr) of the engine occurring in absence of injection and comparing said number of rotations with a threshold value (Nrt) indicating the presence of air alone in the exhaust line to pass to an active state in which there is carried out said operation for obtaining adaptation values (Ot) from the signal (λ) measured by said lambda probe in a determined engine operating phase wherein in said exhaust line there are no exhaust gases.