A dual mode method for controlling the density of a toner image is disclosed for an electrophotographic process. In the first mode, an electrostatic latent image is formed on a photosensitive member from a reference pattern having a predetermined reflectance, the latent image is developed, the density of the developed image is detected, and this density information is used to replenish toner to the developer. A second mode can be actuated in which the photosensitive member is excited to form a region of approximately saturating residual potential which is then developed under a predetermined bias potential, the density of the thus developed image is detected and the density information is used to determine whether the developing step is functioning properly.