Patent ID: 7297240

Claim:
A degradation detection apparatus for an oxygen sensor, comprising: a first judgment value acquirer that calculates an element impedance real value from a value related to an electric power supplied to the oxygen sensor, and that acquires the calculated value as a first judgment value; a second judgment value acquirer which calculates an element temperature estimated value of the oxygen sensor from a factor that affects a temperature of the oxygen sensor, and which acquires the calculated value as a second judgment value; and an abnormality determiner that determines whether the oxygen sensor has an abnormality based on the first judgment value and the second judgment value, wherein the abnormality determiner determines that the oxygen sensor has an abnormality if a relationship between the first judament value and the second judgment value does not agree with a normal temperature characteristic that is exhibited by an element impedance of the oxygen sensor, wherein the oxygen sensor comprises a sensor element that exhibits the temperature characteristic, and a heater for heating the sensor element, wherein the factor that affects the temperature of the oxygen sensor includes at least a factor related to a state of operation of the heater, and wherein the abnormality determiner comprises a heater electrification state detector that detects a state of electrification of the heater, and a sensor element abnormality identifier that, if it is determined that the oxygen sensor has an abnormality in a situation where the heater is not electrified, identifies the abnormality as an abnormality of the sensor element.