On board fault diagnosis is a crucial point for the automotive industry. Recently, new on-board diagnostic system requirements (OBD II) have been enforced on California vehicles and this new legislation will become stricter and stricter from the year 2000 and be-yond. Such requirements will be extended in Europe in the next few years. In fact, the government regulations will impose to monitor vehicles emissions and alert the driver if the exhaust after-treatment system is not properly working. To meet these specifications, sophisticated diagnostic algorithms have to be developed. This paper presents a fault detection strategy on the automotive exhaust after-treatment system in order to fulfil the above mentioned OBD II. This algorithm, based on simple control-oriented models of the three-way catalytic converter and the oxygen sensor, is simple enough for real time applications. The overall strategy has been tuned and validated on the basis of experimental data.
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