<div class="htmlview paragraph">Several factors (changing operator skills, changing legislation, and changing technology among others) are creating the need for improved vehicle diagnostic systems.</div> <div class="htmlview paragraph">There are many difficulties in designing good diagnostic systems that incorporate the optimum compromise between effectiveness in locating a fault, and test hardware overhead. Before such a compromise can be arrived at, it is necessary to move away from the add-on approach to diagnostic hardware, and treat failure detection, isolation, and repair as a total system that pulls together vehicle, dealer, and factory capabilities.</div>