A friend of mine has a Brother HL-2140 Laser Printer and has started having some issues. He's been through at least (probably more) 10-15 toner cartirdges if that helps. Anyways, he called me up today asking me to help him research his current issue. He hates using "bargain toners" becasue they dont last long and generally only uses the TN-360 high yield toners. Hes saying hes barely printed 500 pages and its already giving him a low toner error. The drum has not been replaced ever...would that have anything to do with it? Hes noticed a trend with slowly declining toner output and I guess this is the one that caught his attention since thats vastly below what a toner cartridge should be able to put out.
Perhaps the toner counter didn't reset when he replaced the cartridge. To reset the counter:
start with printer turned off
open front cover
press and hold the white plastic piece on inside top left while turning power back on
once all three printer lights are on, release white plastic piece and then press piece two times
release white plastic piece, wait for lights to come back on, and press six more times
close front cover
wait for printer to reset to solid blue go light
additionally, if he wants to see how much life is left on the toner or the drum unit you and press the go button three times rapidly and it should print out a sheet with all sorts of printer stats on it, including life remaining on the drum and and toner.