Nitrogen oxide (NOx) detector diagnosis procedure, uses comparative values of two signals at different times and default signal when difference drops below permitted threshold level

摘要

The NOx detector (15) diagnosis procedure consists of measuring two values for the signal (NO) from the detector at different times, determining difference between the values, comparing the difference with set threshold levels (SW1 - SW5), and emitting a default signal (FS) if the difference drops below a threshold level. The compared signals can be taken during a lean burn phase of an i.c. engine and at the end of a suppression signal. At least two signal differences are formed, and a default signal is emitted only when the differences are below all the threshold values.