O.sup.2 -sensor fault diagnosis method and apparatus

Abstract

An O.sub.2 -sensor fault diagnosis method and apparatus for detecting a fault of an O.sub.2 -sensor when a feedback control of a fuel supply to an engine is performed by making use of the output of an O.sub.2 -sensor and detecting and identifying a fault of the O.sub.2 -sensor even in the case where the feedback control is invalidated. A microcomputer (24) receives an output of an O.sub.2 -sensor (19) for detecting concentration of oxygen contained in an exhaust gas of an internal combustion engine (1). An ECU (20) controls a quantity of fuel supplied to the internal combustion engine (1) through feedback control in dependence on an output signal of the O.sub.2 -sensor (19). A first decision circuit is provided for deciding whether or not the O.sub.2 -sensor (19) exhibits abnormality on the basis of the output signal state of the O.sub.2 -sensor (19) by forcibly changing the amount of the fuel supplied to the engine during the feedback control, and a second decision circuit is provided for deciding abnormality of the O.sub.2 -sensor (19) in accordance with an abnormality decision process which bears a stronger correlation to the abnormality than the decision performed by the first decision circuit. Fault detection of the O.sub.2 -sensor is possible not only during the feedback control of the fuel supply but also in the state where the feedback control is not performed.

Dependencies are inferred from the claim text.