A malfunction diagnosis system of a printer is provided. A printer controller receives malfunction-related input by the user from an input device, which user input specifies a print defect perceptible to the user. It generates image data representing a test print job in response to the user input specifying the perceptible print defect, and forwards the test print job image data to the printing unit to produce a corresponding test printout. Measurement data output from a sensing device as measured on the test printout is received and analyzed, and information indicative of a cause for the print defect based on the analyzed measurement data output from the sensing device is output.