It is possible the Brother HL-2140 will not reset properly after putting in a new cartridge. You may still have a ‘toner low’ or ‘toner empty’ message. It is possible to manually reset the printer to remove this message:
After changing a DR2100 drum unit in a Brother HL-2140, the printer’s page count needs to be reset. This will turn off the drum warning light on the printer.
Simply open the front cover, and hold the “GO” button until all four LED’s are lit. Release the “GO” button and close the front cover.
Youtube Video: Drum Reset
Youtube Video: Change Toner Cartridge