DIAGNOSIS The printer has detected a fault with the drum unit. This is often triggered by a dirty or faulty drum shutter mechanism.
FIX Power off the printer. Open the front cover. Remove the toner cartridge and drum unit assembly. Inspect the green drum roller for scratches or toner spill. Wipe the roller gently with a lint-free cloth. Locate the gray plastic shutter on the drum unit's side. Slide it back and forth several times to clear debris. Reinstall the drum unit and toner cartridge. Close the cover. Power on.
IF THAT DIDN'T WORK The drum unit life may be exhausted. The printer tracks drum usage internally. To check, print a settings report. Navigate: Menu > Reports > Settings. The report will show the drum counter. If near or at 100%, the drum unit requires replacement.
HEADS UP Do not expose the drum unit to direct light for more than a few minutes. It is photosensitive and can be permanently damaged.