Brother HL-2040

[E Winter]

Yeah, just reset the toner detection lever - it's a white thingy located at one side of the cartridge. You'll need to turn the dev-roller backwards while forcing the lever a bit so it moves about 45 degrees.

[good]

If resetting doesn't help then sometimes the toner is the problem.

Did you replace it with a generic or oem toner?

Sometimes generic toner causes this problem.