| 摘要 |
A method for determining malfunction of a nitrogen oxide sensor compares a nitrogen oxide amount detected by the sensor with a predetermined value of nitrogen oxide. If the difference between the predetermined value and the amount detected by the sensor is within a predetermined range, the method determines whether an engine is in a steady state. If the engine is in a steady state, the method changes one or more engine control parameters, thereby varying an actual nitrogen oxide amount. After changing the parameters, the method determines whether the amount detected by the sensor changes. The method determines that the sensor is malfunctioning if the amount detected by the sensor does not change. A selective catalytic reduction system includes a first nitrogen oxide sensor, a selective catalytic reduction apparatus, and a second nitrogen oxide sensor, all disposed in an exhaust pipe. A control portion performs the above-described method.
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