Patent ID: 7416649

Claim:
An oxygen concentration detection system having an oxygen sensor comprising a sensor element including a combination of an oxygen pump cell and an oxygen-partial-pressure detection cell; a control circuit connected to the sensor element via wiring lines adapted to control the oxygen pump cell such that the output voltage of the oxygen-partial-pressure detection cell is maintained at a predetermined value, the oxygen sensor detecting the concentration of oxygen contained in a gas to be measured having an oxygen concentration within a predetermined range, and the oxygen concentration detection system outputting measurement signals of a plurality of types, including a first signal corresponding to a magnitude of current flowing through the oxygen pump cell, a second signal corresponding to an electric potential of the oxygen-partial-pressure detection cell, and a third signal corresponding to a resistance of the oxygen-partial-pressure detection cell, the oxygen concentration detection system comprising: anomaly detection means for detecting a sensor anomaly by determining whether at least one of respective levels of signals which represent electric potentials at different portions of the sensor element, the wiring lines, and the control circuit falls within a predetermined range; modification means for issuing a first instruction when the anomaly detection means does not detect an anomaly, the first instruction indicating non-detection of an anomaly, and for issuing a second instruction when the anomaly detection means detects a sensor anomaly, the second instruction corresponding to the detected anomaly; and output means for through-outputting the measurement signals when the modification means outputs the first instruction signal and for outputting a selected measurement signal modified to have a level outside the corresponding range within which the level of the selected measurement signal varies in a normal state.