A toner maintenance system for an electrophotographic developer unit, including a sump for storing a quantity of developer material comprised of carrier and toner material; a first member for transporting a mixture of developer material and toner particles from the sump, the first member having a voltage applied thereto; a metering blade, positioned closely adjacent to the first member to maintain the compressed pile height of the developer material on first member at a desired level; and a sensor device for measuring the current between the first member and the metering blade, and generating a signal indicative thereof.