TABLE OF CONTENTS On-board diagnosis of car engines has become increasingly important because of environmentally based legislative regulations such as OBDII (On-Board Diagnostics-II) [17]. Other reasons for incorporating diagnosis in vehicles are reparability, availability and vehicle protection. Today due to the legislations, the majority of the code in a modern engine management system is dedicated to diagnosis.
Diverse diagnosis techniques are used in production vehicles [124] [57], and the selection of methods depends on the requirements of the more and more restrictive regulations. The simplest forms are based on limit checking of sensors and on active diagnosis. Active diagnosis means that during special operating conditions, the engine is manipulated in such a way that possible faults will be revealed. This is for example used heavily during idle. However, such techniques may be insufficient to fulfill the more restrictive regulations. Further, sometimes the lack of a good diagnosis schemes have forced engineers to choose suboptimal engine control solutions to accommodate the diagnostic requirements. It is therefore desirable to use new diagnosis techniques that perform better and do not rely on special operating conditions and active diagnosis. This leads to the field of model based diagnosis where more physical knowledge about the system is utilized.
The purpose of this chapter is to give an introduction to engine diagnosis. It starts in Section 6.1 with a background in engine diagnosis, and continues in Section 6.2 with a description of one example of an actual regulation, namely the OBDII by the California Air Resource Board [17].
