Hold the MPF tray media flag to cause the indicator light to switch ON. The light ON would indicate media is present.
Does the light turn off and on?
The sensor is functioning properly. See next step.
Contact Lexmark support for further diagnosis.
Does the media flag move freely and with little resistance?
Does the light switch OFF without media being present or loaded into the tray?
Continue testing to see if the error returns.
Try to push or pull the flag downward into its socket (fulcrum, pivot) to snap the sensor arm back into place.