Patent attributes
An apparatus for diagnosing malfunctioning which is applied to an internal combustion engine having a catalyst, an air-fuel ratio sensor, and an oxygen sensor is disclosed. The apparatus diagnoses whether the oxygen sensor is malfunctioning on the basis of a change in an output value of the oxygen sensor within a predetermined period of time after the output value has started changing towards a lean side after the start of fuel cutoff. The apparatus is provided with a first determination section and a second determination section. The first determination section determines whether fresh air has reached the air-fuel ratio sensor after the start of the fuel cutoff. The second determination section determines whether or not to carry out diagnosis of malfunctioning on the basis of the output value of the oxygen sensor immediately after the first determination section has determined that fresh air has reached the air-fuel ratio sensor.
