Patent ID: 7021300

Claim:
A deterioration failure diagnostic apparatus for an exhaust gas sensor disposed in an exhaust passage of an internal-combustion engine, said sensor producing outputs responsive to exhaust gas from the engine, comprising: detecting signal generating means for generating a detecting signal and multiplying the generated signal to a first basic fuel injection amount to produce a second basic fuel injection amount; feedback representative value calculating means for calculating a feedback representative value based on a feedback correction coefficient used at a normal operation time and multiplying the feedback representative value to the second fuel injection amount to produce a final fuel injection amount to be injected to the engine; and exhaust gas sensor evaluating means for extracting from an output of the exhaust gas sensor of the engine a frequency response corresponding to the detecting signal, the output being in response to the final fuel injection amount, said exhaust gas sensor evaluating means determining a condition of the exhaust gas sensor based on the extracted frequency response.