A method for control of dosage of a reducing agent into an exhaust stream from an engine , said reducing agent being used for reduction of nitrogen oxides NO x in one or more reduction catalysts of an exhaust treatment system arranged for treating said exhaust stream , characterized by: - determining at least one sensor signal S NOx from at least one nitrogen oxides NO x sensor arranged downstream of at least one of said one or more reduction catalysts as at least one sensor correction value S NOx_corr , respectively, if: - said engine revolves without fuel supply; - an exhaust mass flow M exh · is greater than an exhaust mass flow threshold M exh _ th · ; M exh · > M exh _ th · ; and - said at least one sensor signal S NOx has had a value smaller than a sensor signal threshold S NOX_th ; S NOx <S NOX_th ; during at least a predetermined time period T con , wherein the time amounting to the predetermined time period T con , starts running as soon as the engine is revolving and wherein the predetermined time period T con has a value large enough for ensuring that the at least one sensor signal S NOx , only includes an offset error; - determining at least one adjusted sensor signal S NOx_adj based on said at least one sensor signal S NOx and said at least one sensor correction value S NOx_corr , respectively; and - controlling said dosage of said reducing agent based on said at least one adjusted sensor signal S NOx_adj . - determining at least one sensor signal S NOx from at least one nitrogen oxides NO x sensor arranged downstream of at least one of said one or more reduction catalysts as at least one sensor correction value S NOx_corr , respectively, if: - said engine revolves without fuel supply; - an exhaust mass flow M exh · is greater than an exhaust mass flow threshold M exh _ th · ; M exh · > M exh _ th · ; and - said at least one sensor signal S NOx has had a value smaller than a sensor signal threshold S NOX_th ; S NOx <S NOX_th ; during at least a predetermined time period T con , wherein the time amounting to the predetermined time period T con , starts running as soon as the engine is revolving and wherein the predetermined time period T con has a value large enough for ensuring that the at least one sensor signal S NOx , only includes an offset error; - said engine revolves without fuel supply; - an exhaust mass flow M exh · is greater than an exhaust mass flow threshold M exh _ th · ; M exh · > M exh _ th · ; and - said at least one sensor signal S NOx has had a value smaller than a sensor signal threshold S NOX_th ; S NOx <S NOX_th ; during at least a predetermined time period T con , wherein the time amounting to the predetermined time period T con , starts running as soon as the engine is revolving and wherein the predetermined time period T con has a value large enough for ensuring that the at least one sensor signal S NOx , only includes an offset error; - determining at least one adjusted sensor signal S NOx_adj based on said at least one sensor signal S NOx and said at least one sensor correction value S NOx_corr , respectively; and - controlling said dosage of said reducing agent based on said at least one adjusted sensor signal S NOx_adj . <EOS>