A method for operating an internal combustion engine is described, in which the ambient pressure is determined by an ambient pressure sensor and the pressure in an intake manifold of the internal combustion engine is determined by an intake manifold pressure sensor. In this method the reliability performance of the ambient pressure sensor is checked by comparing the ambient pressure to a starting value that is obtained by the intake manifold pressure sensor before a starting process of the internal combustion engine. The comparison is only performed if a preceding check of the intake manifold pressure sensor yields the result that it is operational.