We have a similar problem. Machine shows 11% toner regardless of number of jobs printed. New cartridges (we have used four) show all the same percentage and estimated pages remaining starts at zero.
With every page printed, the estimated pages remaining increases! It's like there is a flipped sign bit in the counter (I suspect).
Cold Reset, HDD Init, NVRAM Init, Replaced the formatter and hard drive. Updated firmware. NVRAM init (just in case).