The Brother HL-3140CDW printer is a nifty, inexpensive colour laser printer (at least it was when I bought it). However, Brother has a bad practice of telling you that your toner cartridges are low when they're not.
To work around this, you can easily reset the toner counter, extending the life of your cartridges. It's pretty easy, it's just not in the user manual.
- Power on your printer.
- Life open the door.
- Press and Hold Cancel then Secure, together, and release.
This should put your printer into the Reset menu.
- Use the UP and DOWN arrows to navigate to the toner cartridge you want to reset.
- Press OK to select it.
- Press UP to reset.
- Repeat for each toner cartridge you want to reset. The LCD will show Accepted after the reset has completed.
Close the printer door / lid when you're done, and then do a happy happy dance, because using this menu, I've been able to more than double the lifespan of my toner cartridges. This makes this machine a really good printer investment.
(Credit to this video for the instructions.)