Patent ID: 7574905
Filing Date: 2009-08-18
Classification: F02D,G01M

Abstract:
1. An apparatus for diagnosing malfunctioning, which is applied to an internal combustion engine having a catalyst provided in an exhaust passage for purifying exhaust, an upstream oxygen concentration sensor provided in a section of the exhaust passage on the upstream side of the catalyst, and a downstream oxygen concentration sensor provided in a section of the exhaust passage on the downstream side of the catalyst, and wherein the apparatus diagnoses whether a downstream oxygen concentration sensor is malfunctioning on the basis of a change in an output value of the downstream oxygen concentration sensor within a predetermined period of time after the output value has started changing toward a lean side after the start of fuel cutoff, the apparatus comprising: a first determination section for determining whether fresh air has reached the upstream oxygen concentration sensor after the start of the fuel cutoff; and a second determination section for determining whether or not to carry out the diagnosis of malfunctioning on the basis of the output value of the downstream oxygen concentration sensor immediately after the first determination section determines that fresh air has reached the upstream oxygen concentration sensor.