| 摘要 |
A method and system for diagnosing a failure of a rear oxygen sensor is provided. The sensor is determined to have failed if the difference between a maximum output value and a minimum value of the rear oxygen sensor is less than a first value, and if it is not, it is determined whether the difference is between the first value and a second value. If so, the air/fuel mixture is controlled to be richer than a stoichiometric air/fuel ratio for a predetermined period. Then, an output values of a front oxygen sensor and the rear oxygen sensor are respectively compared to first and second threshold values. If the output value of the front oxygen sensor is greater than the first threshold value, and the output value of the rear oxygen sensor is less than the second threshold value, it is determined that the rear oxygen sensor has failed.
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