Abstract: A print system and a method for detecting and correcting underperforming LEDs in-line of a 3D object printer are disclosed. For example, the print system includes a plurality of printheads arranged in a two-dimensional array, a curing light source, an inline detection and correction (IDC) system, a movable member to hold an object and a test plate and a controller to control movement of the movable member to move the object and the test plate past the array of printheads, to operate the plurality of printheads to eject a marking material onto the object as the object passes the two-dimensional array of printheads, to operate the curing light source apply energy to the test plate and to cure the marking material, and to operate the IDC system to read the test plate to confirm that the curing light source is operating correctly based on a reading of the test plate.