Method of diagnosing deterioration of resin part

A method of diagnosing a deterioration of a resin part, the method estimating a degree of progress of the deterioration of the resin part incorporated in a vehicle, the method comprising:

• fabricating a deterioration detection part by adding a detection additional member to the resin part, the detection additional member being faster in progress of a deterioration than the resin part and being easier to detect the progress of the deterioration than the resin part, the adding the detection additional member to the resin part comprising bonding the detection additional member to a surface of the resin part or insert-molding the detection additional member to the resin part;
• incorporating the deterioration detection part into a portion, of the vehicle, where the resin part is to be incorporated;
• detecting, after an elapse of a predetermined period of time, a degree of the progress of the deterioration of the detection additional member added to the resin part;
• and
• estimating, based on correlation data obtained in advance, the degree of the progress of the deterioration of the resin part, the correlation data being data on a correlation between the deterioration of the detection additional member and the deterioration of the resin part.