ABSTRACT
Enabled by the increasing advances in electronics and microprocessor software development, on-board diagnostics (OBD) has been developed over recent years and is now implemented by all major motor vehicle manufacturers. Fundamentally, a contemporary microprocessor-based on-board diagnostics or OBD system is intended to self-diagnose and report when the performance of the vehicle's emissions control systems or components have degraded. This chapter discusses the origins of OBD in the USA and covers the fundamentals of some of the OBD systems employed on mainstream petrol/gasoline vehicles. It also explores the concept of how the OBD system is divided into a series of software-based serviceability indicators, known as ‘OBD monitors’. An important part of any OBD system is the system monitors and associated readiness flags. The European on-board diagnostics system is designed, constructed and installed in a vehicle such as to enable it to identify types of deterioration or malfunction over the entire life of the vehicle.
