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摘要

An engine system includes a nitrogen oxide (NOx) estimation module and a diagnostic module. The NOx estimation module estimates an amount of NOx in an exhaust gas produced by an engine based on a predetermined function of a position of at least one of a camshaft phaser and an exhaust gas recirculation (EGR) valve. The diagnostic module determines a state of at least one of the camshaft phaser and the EGR valve based on a predetermined threshold and a difference between the estimated amount of NOx and an actual amount of NOx in the exhaust gas measured by a NOx sensor.