A reductant delivery system for an internal combustion engine is arranged to inject a reductant into the exhaust aftertreatment system upstream of a catalytic device. A method for controlling the reductant delivery system includes operating the fluidic pump at a preset state, operating the injector at a zero-flow state, and monitoring, via a pressure sensor, a pressure in the reductant delivery system upstream of the injector to determine a zero-flow pressure. The injector is activated under a preset condition and an actual pressure drop upstream of the injector is monitored. A pressure drop deviation is determined based upon the actual pressure drop upstream of the injector and an expected pressure drop upstream of the injector. An adjustment to the activation of the injector is determined based upon the pressure drop deviation, and the injector is controlled based upon the adjustment.