Patent ID: 7987661

Claim:
A method for determining malfunction of a nitrogen oxide sensor, comprising: comparing a nitrogen oxide amount detected by the sensor with a predetermined value of nitrogen oxide; if a difference between the predetermined value and the amount detected by the sensor is within a predetermined range, determining whether an engine is in a steady state; if the engine is in a steady state, changing one or more engine control parameters, thereby varying an actual nitrogen oxide amount; after changing the parameters, determining whether the amount detected by the sensor changes; and determining a malfunction of the sensor if the amount detected by the sensor does not change; wherein the parameters comprise at least one member selected from the group consisting of pilot injection flux, pilot injection timing, main injection flux, main injection timing, exhaust gas recirculation amount, and combinations thereof; and wherein changing the parameters comprises: determining whether an engine speed is in a middle/low range; if the engine speed is in the middle/low range, determining whether a load is on or off, and whether a coolant temperature is within a predetermined range; and changing one or more of the parameters based on the coolant temperature and whether the load is on or off.