Brother MFC-8440 B - Manual (Page 189)

TROUBLESHOOTING AND ROUTINE MAINTENANCE 12 - 28
Replacing the toner cartridge
The MFC can print up to 6,700 pages using a high yield toner
cartridge. When the toner cartridge is running low, the LCD shows
Toner Low
. The MFC is supplied with a standard toner cartridge
that must be replaced after approximately 3,500 pages. Actual page
count will vary depending on your average type of original (i.e.,
standard letter, detailed graphics).
Discard the used toner cartridge according to local regulations,
keeping it separate from domestic waste. Be sure to seal the toner
cartridge tightly so toner powder does not spill out of the cartridge. If
you have questions, call your local waste disposal office.
We recommend that you clean the MFC when you replace the toner
cartridge.
It is a good idea to keep a new toner cartridge ready for use
when you see the Toner Low warning.