Page 367 - Understanding Automotive Electronics

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10 DIAGNOSTICS

The service bay diagnos- Among the many capabilities of the technicians’ terminal is its ability to
tic system can be readily store and display the diagnostic charts that appear in the shop manual.
updated with new ser- Whenever a fault is located, the appropriate chart(s) are automatically displayed
vice bulletins. for the mechanic. This capability greatly increases the efficiency of the
diagnostic process. In addition, the GM-CAMS computer can store all of the
data that is associated with the diagnostic procedures for several vehicles and
then locate and display, virtually instantaneously, each specific procedure as
required. Furthermore, updates and the most recent service bulletins are
brought into the mechanics’ terminal over the phone network so that
mechanics lose no time trying to find the most recent data and procedures for
diagnosing vehicular electronic systems.
In addition to storing and displaying shop manual data and procedures, a
computer-based garage diagnostic system can automate the diagnostic process
itself. In achieving this objective, the technicians’ terminal has the capability to
incorporate what is commonly called an expert system.
EXPERT SYSTEMS

An expert system is a form Although it is beyond the scope of the present book to explain expert
of artificial intelligence systems, it is perhaps worthwhile to introduce some of the major concepts
that has great potential involved in this rapidly developing technology. An expert system is a computer
for automotive diagno- program that employs human knowledge to solve problems normally requiring
sis. human expertise. The theory of expert systems is part of the general area of
computer science known as artificial intelligence (AI). The major benefit of
expert system technology is the consistent, uniform, and efficient application of
the decision criteria or problem-solving strategies.
The diagnosis of electronic engine control systems by an expert system
proceeds by following a set of rules that embody steps similar to the diagnostic
charts in the shop manual. The diagnostic system receives data from the
electronic control system (e.g., via the ALDL connector in the GM-CAMS) or
through keyboard entry by the mechanic. The system processes this data
logically under program control in accordance with the set of internally stored
rules. The end result of the computer-aided diagnosis is an assessment of the
problem and recommended repair procedures. The use of an expert system for
diagnosis can significantly improve the efficiency of the diagnostic process and
can thereby reduce maintenance time and costs.
An expert system takes The development of an expert system requires a computer specialist who
information from is known in AI parlance as a knowledge engineer. The knowledge engineer must
experts and converts this acquire the requisite knowledge and expertise for the expert system by
to a set of logical rules. interviewing the recognized experts in the field. In the case of automotive
electronic engine control systems the experts include the design engineers as
well as the test engineers, mechanics, and technicians involved in the
development of the control system. In addition, expertise is developed by the
mechanics who routinely repair the system in the field. The expertise of this
latter group can be incorporated as evolutionary improvements in the expert

354 UNDERSTANDING AUTOMOTIVE ELECTRONICS