The present invention provides for a method and device for monitoring an ambient humidity sensor in a combustion engine, where the monitoring of the ambient humidity sensor is made by comparing the ambient humidity measured by said humidity sensor and an ambient humidity determined from an oxygen measurement of at least another sensor in the engine system, such as a NOX, or Lambda and/or an oxygen sensor. Said comparison is made using an offset of the oxygen signal reading of said at least another sensor, in a fuel cut condition where the drift or offset of said another sensor is related to the variation of the ambient humidity.