A closed-loop piezoelectric pump is disclosed for use in a fluid delivery system. The pump housing includes a movable diaphragm that defines a pumping chamber within the pump housing, the pumping chamber having an inlet for admitting fluid and an outlet for emitting fluid. A piezoelectric transducer is coupled to the moveable diaphragm and operates to produce a pumping action by varying the volume of the pumping chamber. The piezoelectric transducer may be used to generate an acoustic pressure pulse within the fluid delivery system and to sense reflections of the acoustic pressure pulse caused by impedance changes downstream of the pump. Properties of the fluid path downstream of pump may be determined from the characteristics of the sensed reflections.