Check the installation of the fuser unit:

1. Ensure that the fuser unit is inserted correctly and that it is firmly held in position
2. Power off the printer and unplug it, then wait for 5 minutes
3. Power on the printer and check that the fuser unit is recognized

1. Remove the fuser unit from the printer
2. Carefully inspect the fuser unit for any physical defects
3. Clean the inside of the printer to ensure it is free from obstruction
4. Reinsert the fuser unit into the printer and power on the printer and check that it is now recognized