Diagnosing i.c. engine EGR valve performance

摘要

A method and system for diagnosing a condition of an EGR valve 16 used in an engine system is disclosed. The method includes establishing whether a change in NOx emissions has occurred and determining the condition of the EGR valve 16 based upon a function of the change in NOx emissions. A time rate of change in NOx measured by the NOx sensor may be determined and compared, eg by statistical analysis, with a predetermined expected time rate of change. Instances when samples of the measured NOx are greater than an expected maximum and less than an expected minimum may be determined. The method may also include determining whether the NOx sensor is faulty and the EGR condition determining includes determining whether the NOx sensor is faulty.