Patent ID: 8195354

Claim:
A diagnostic device for diagnosing a condition of a detecting unit which detects, in a normal condition, a differential pressure of an exhaust gas between upstream and downstream sides of an exhaust emission control device disposed in an exhaust system of an internal combustion engine and detects no differential pressure of the exhaust gas in a fault condition, comprising: at least one programmed processor in communication with associated memory, input and output ports and configured to include: an operation condition judging unit that judges whether the engine is operated in a low flow rate region or in a high flow rate region, a flow rate of the exhaust gas passing through the exhaust emission control device in the high flow rate region being higher than that in the low flow rate region; a detection result obtaining unit that obtains a first detection result of the detecting unit when the operation condition judging unit judges the engine to be operated in the low flow rate region and obtains a second detection result of the detecting unit when the operation condition judging unit judges the engine to be operated in the high flow rate region; and a diagnostic unit that judges from a difference between the first and second detection results obtained by the detection result obtaining unit whether the detecting unit is in the normal condition or in the fault condition, wherein the detection result obtaining unit is adapted to obtain a plurality of first detection results during the operation of the engine in the low flow rate region and to obtain a plurality of second detection results during the operation of the engine in the high flow rate region, and the diagnostic unit is adapted to judge that the detecting unit is in the fault condition when a difference between a minimum value of the first detection results and a maximum value of the second detection results is equal to or smaller than a predetermined value.