I've had many InkJet printers, and a couple of old simple B&W Laser printers, but since getting my new colour laser, I've
learnt something new!! It's only a few months old, (Brother), and have only printed about 50 or so pages. Now it comes
up occasionally, with a warning msg on my screen, which I found out was saying the "Wast Toner Cartridge" is about to
expire, and needs replacing!
Up until now, I had never even 'heard' of such an item! (Though I now know it's use).
To anyone else, uninitiated/curious, after research it seems this is a common false warning, from those 'sensors'.
YouTube has numerous videos of how to clean them, and reset them, without any expensive replacement. Grrr...