There is a little reset routine to remove the toner low warning light on some Brother printers after replacing the toner cartridge

Reset brother 2250dn toner low warning

1. Power Unit off
2. Open front cover
3. Press and hold GO and turn power on
4. When all 3 lights lit release and press GO twice
5. All lights turn solid
6. With all solid, press GO 5 times
7. Ready light goes red
8. Close door