DIAGNOSIS A small piece of paper tore off and is stuck deep in the paper path, likely behind the print head carriage. The sensor is still tripped.
FIX Unplug the printer. Open the rear cover. Look for a small scrap in the rollers near the duplex unit. Use plastic tweezers, not metal. Remove any debris. Close the cover and power on.
IF THAT DIDN'T WORK The jam could be under the print head. Move the print head to the center manually. Inspect the area under and around it for tiny paper shreds.
HEADS UP Forcing the rear cover or carriage can break the plastic latches. Always unplug first to avoid motor damage.