I have a brother HL-4040CN colour laser printer, and it just started saying that ALL 3 colour toner cartridges had run out (and would refuse to print)

Now, I know I print more yellow than any other colour, so telling me that all 3 need to be replaced it just a lie!

I find out that the cartridges that I use are compatible with the following numbers: TN-115, TN-135, TN-155, TN-175

I had a look at the cartridges, and on the side, is a small circular “window” of clear plastic, where I assume the printer shines a light, to see if it gets to the other side (and then guess how much longer the cartridge will last before it actually runs out.

Obviously their guess is wrong (and I suspect its deliberately wrong… for financial reasons… it means Brother gets to sell more toner).

This is particularly annoying, when I see the clear window is half way between the top and the bottom of the cartridge.

So after a bit of searching, I find a way to trick the printer into using all the toner:

1. Place a small piece of dark electrical tape over the clear window. Don’t use anything clear or shiny, as the printer might receive a “false empty” signal. I just did it to all 4 cartridges… even the black one that still had plenty of toner.
2. With the front cover still open, press and hold the “cancel” button.
3. while holding the cancel button, press the reprint button.
4. You should now see  Reset Parts Life menu in the LCD screen.
5. Use the up/down arrow to select the cartridge life you want as follow:
6. B.TNR-S = Black standard toner
7. B.TNR.H = Black high-yeild toner
8. C.TNR-S = Cyan standard toner
9. C.TNR.H = Cyan high-yeild toner
10. M.TNR-S = Magenta standard toner
11. M.TNR.H = Magenta high-yeild toner
12. Y.TNR-S = Yellow standard toner
13. Y.TNR.H = Yellow high-yeild toner

So I reset all colours to high-yeild, and now I can use the printer until all the toner is truly finished.

I close the front cover, and I can now print again.