Abstract: An apparatus is disclosed for continuously sampling, at a point downstream of the air cleaner, the normally clean air entering an air induction system of a diesel engine to produce a signal indicating a leakage malfunction condition in the air induction system by measuring dust/particulate matter. The disclosed apparatus includes an arrangement in the form of a sample collector assembly for obtaining a representative sample of leakage particulates within the diesel engine intake system, a measurement assembly for the quantification of the dust/particulates by optical methods, a signal conditioning assembly (200), a processor (300), and a remote annunciation assembly (400).