Provided is a method for diagnosing exhaust sensors, where at least one substance resulting from combustion is reduced by an additive. A first sensor intended to measure an occurrence of said substance upstream said supply of additive, and a second sensor intended to measure an occurrence of said substance downstream said supply of additive. The method comprises: determining whether the locations of said first and second sensors are reversed by: determining if a second measurement value of said second sensor exceeds a corresponding first measurement value of said first sensor at least to a first extent, and when this condition occurs, determining that the locations of said first and second sensors sensor are reversed, said measurement values are determined when a supply of additive is set to obtain at least a first reduction of said at least one substance to be reduced.