At first you get the “Toner Low” and then the “Toner Life End” message. The following instruction shows how to reset low toner message on your Brother MFC 9840 CDW:
1. Turn on the printer.
2. Push the button on the front of the printer to open the cartridge door. Do not remove the cartridges.
3. Push the Clear/Back button and hold till to bring up a reset menu. There are 8 different toner functions ( two Black, two Cyan , two Magenta, and two Yellow).
4. For each of these eight functions in turn, push the O.K. button and then push it again to indicate ‘Reset’. After a few seconds, it will say ‘Accepted’ and will then display a message that the cover is open.
5. Repeat steps 3 and 4 for each of the 8 toner functions.
6. When finished, close the door and the status bar will be reset to normal with no error message.