Patent ID: 6877498

Claim:
An oxygen sensor deterioration diagnosis apparatus comprising: an oxygen sensor provided in an exhaust system of an internal combustion engine and for outputting a signal corresponding to an oxygen concentration in an exhaust gas; an air-fuel ratio control unit for controlling an air-fuel ratio to a vicinity of a theoretical air-fuel ratio on the basis of an output of the oxygen sensor; an operation state detection unit for detecting an operation state of the internal combustion engine; an inversion period measurement unit for detecting an inversion period of the signal outputted by the oxygen sensor; an oxygen sensor deterioration diagnosis unit for performing a deterioration judgment by comparing, when the operation state of the internal combustion engine detected by the operation state detection unit is a specified operation state, the inversion period of the output signal of the oxygen sensor measured by the inversion period measurement unit with a previously set deterioration judgment period; and a deterioration diagnosis inhibiting unit for inhibiting, when the operation state detection unit detects the operation state of the internal combustion engine having an influence on the inversion period of the output signal of the oxygen sensor, the measurement of the inversion period by the inversion period measurement unit in a period of time of the detection.