A diagnostic apparatus for a powder coating material pump includes a detector that uses pressure or flow to detect a fault in the pump, the diagnostic apparatus being external the pump, internal the pump or a combination of external and internal the pump. Another diagnostic device is provided for a powder coating material pump, and includes a light source in close proximity to the pump, the light source having an on condition and an off condition wherein one or both of the on condition and off condition provides information about the pump performance. An exemplary pump is a dense phase powder coating material pump.