Abnormality determination apparatus and method for oxygen sensor

摘要

An abnormality determination apparatus for an oxygen sensor provided on the downstream side of a catalyst includes: a first determination portion that determines whether amount of decline in output value of the oxygen sensor during a period from when amount of intake air or exhaust gas declines before a fuel cut is started to when the fuel cut is started is smaller than a reference amount of decline; a second determination portion that determines whether degree of change in the output value when the output value changes from a first reference value to a second reference value that shows a leaner state than the first reference value is more gradual than a set degree of change after the fuel cut is started; and a third determination portion that determines whether the oxygen sensor is abnormal based on determinations by the first determination portion the second determination portion.