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Because of legislative regulations like OBDII, on-board diagnosis has gained much interest lately. A model based approach is suggested for the diagnosis of the air intake system of an SI-engine. Important research issues are modeling concepts, residual generation and evaluation, overall performance, and limiting factors. The diagnosis system is based on a non-linear semi-physical model and uses a combination of different residual generation methods. It is capable of detecting and isolating faults in the throttle actuator, throttle sensor, air mass now sensor and manifold pressure sensor. The scheme is experimentally validated on a real production engine.

Many model based solutions to diagnosis problems in SI-engines have been discussed in literature. However most presented methods are useful only for a specific class of faults. Here a systematic and more general method is presented. With this method, which is based on a structure of hypothesis tests, it is possible to diagnose a large variety of different types of faults. The method is applied to the diagnosis of sensor-faults and leakage in the air-intake system of an SI-engine. The features of the method are demonstrated by using experiments on a real SI-engine. The experiments show that the method is capable to diagnose both leakage and different types of sensor faults. Both detection and isolation are considered. It is for example possible to distinguish between a manifold leak and a manifold pressure sensor fault.