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Welcome to General Diagnostics at

Useful Methods For Diagnosis And Problem Solving

By Rev. Bill McGinnis, Director - Internet Church Of Christ -
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The purpose of this website is to develop and share some General Diagnostic methods which will apply to many different kinds of diagnostic problems. My particular specialty is Automobile Diagnostics, but I have found that the same general methods which work in automobile diagnostics will also work in most other areas where any kind of diagnosis is needed, such as medicine and computer sytems, and many more.

Ever since some early person first asked the question,"Why?," we humans have been wrestling with the profound concepts of Truth and Causation. "What is truth?" And "Why do things happen?" These are huge and weighty questions, and better minds than mine have fallen short in trying to understand them. I, too, have struggled to find answers to these ultimate questions, and I have given up trying to figure them out for myself.

What I have tried to do, however, is to figure out why particular things have gone wrong in particular situations. And I have found a few concepts which seem to be quite useful for this task. So instead of struggling with the impossible questions, such as the ever-famous "What is truth?," I have settled for the more attainable (and more useful) question, "How did this happen here?"

This page presents these concepts to you, in the hope that you, too, may find them useful. Following my general policy in such matters, I am placing this document in the Public Domain, so that anybody may use it, develop it, modify it any way he chooses. That's how we humans make progress: by improving on the work of others.

I hope this information will be useful to you.

                         Rev. Bill McGinnis, Director


These concepts are nothing more than mental devices we use to understand things. They do not need to conform perfectly with physical reality or with all the possible philosophical niceties. It is good enough for our purposes if they work for us to help us solve our problems. Here are the most important of these concepts, as I see them:

All things which work together to accomplish any particular task make up the SYSTEM of that task. So, for instance, in a car, the braking system is made up of all the parts of the car which work together to accomplish the task of braking. And the ignition system is made up of all the parts of the car which work together to accomplish the task of ignition, that is, creating the spark which ignites the fuel/air mixture in a gasoline engine. In the human body, the digestive system is made up of all the parts which accomplish the task of digestion; and the circulatory system is made up of all the parts which accomplish the task of circulating the blood.

All systems anywhere can be understood in the same way: - the parts which work together to accomplish a task make up the system of that task. Please note that the same part can be a part of more than one system. For example, the oxygen sensor is part of the exhaust system, part of the emissions control system, and part of the powertrain control system in a car. Also please note that systems can overlap each other. For instance, the air conditioning system and the heating system are both parts of the temperature control system.

In fact, the whole idea of "systems" is nothing more than a mental device we use to understand how various processes work. Therefore, there can be no such thing as a "List Of All Systems In A Car," because such a list would be practically infinite in length, going down to the level of perhaps the "Right Front Doorlock Lever Retaining System." The number of "systems" would be exactly the same as the number of tasks performed in the car, and that number is very, very large.

For human convenience, we sometimes resort to the Aristotelian technique of "mutally exclusive and exhaustive" classification, which demands that everything under consideration be assigned to one and only one place. So then we have "systems" and "sub-systems" and "sub-sub-systems," all very neatly putting each item in one and only one place. But I never liked mutually exclusive and exhastive classification very much because it forces Creation into boxes where it doesn't fit. See how the Zoologists struggle to fit flying reptiles into their mutually-exclusive and exhaustive categories! Better, I think, to consider each system on its own, without regard for how it fits into a pre-established organizational structure.

2. NORMAL AND ABNORMAL STATES - Everything about a system is either in a "normal" state or an "abnormal" state. Either the car's brakes are acting normally or they are not. Either the person's digestive system is working normally or it is not. Either the spacecraft's propulsion system is running normally or it is not. Either the oxygen sensor is performing normally or it is not. Either the heart is working normally or it is not. Either the transmitter is working normally or it is not.

Used in this way, "normal" means acceptable, they way they are supposed to be, okay. "Abnormal" means not acceptable, not the way they are supposed to be, not okay. Every thing about a system, even down to the tiniest little bolt in a car, can be categorized as either "normal" or "abnormal." The purpose of all system repair is to correct abnormal states and restore the system to its normal state of operation.

3. NORMAL AND ABNORMAL EVENTS - An "event" is when something happens: a spark plug fires, the heart contracts, a fuel injector opens, a relay closes, the brake caliper squeezes. An event is a change of state, from one condition to another. A "normal event" occurs when something happens just as it is supposed to happen: the headlights come on when the switch is turned on, the engine valves open and close at their proper times. An "abnormal event" is when something happens that is not supposed to happen: the engine quits unexpectedly, the artery becomes clogged, the alternator makes a funny noise. All system complaints can be described and understood in terms of abnormal events: some things are happening which are not supposed to happen, and someone has noticed them. If all the states are normal, all the events will then be normal, and there will be no complaints. Problems solved!

4. UPSTREAM AND DOWNSTREAM - Any process can be understood as a sequence of related events and states happening over time within a context. The context is all of the other events and states which exist at that moment in time. The earlier events and states in a process are considered to be "upstream" from the later events and states, which are considered to be "downstream." Any abnormal event or state downstream must have been caused by abnormal event(s) or state(s) upstream from it.

5. THE NORMAL PROCESSES - A normal process is one in which all events and states are normal. It is necessary to understand the normal processes in a system in order to recognize and understand the abnormal events and states which may occur and need to be corrected.

6. LEVELS OF ABSTRACTION - Processes can be understood and described in different levels of abstraction. A high level of abstraction is one in which the process is summarized, with very few details. Here is a process description in a very high level of abstraction: "You push on the brake pedal and the car slows down and stops." Here is another one: "The heart contracts, and blood is forced throughout the circulatory system." A low-level description of the very same processes might take five thousand words, providing much detail about the operation of the various parts of the systems.

7. CAUSATION - In System Diagnostics, we are looking for the causes of abnormal system events, in order to correct them and bring all processes back to normal operation. So we do not need to address the entire philosophical question of "causation," but only those parts of it which we need in order to understand the causes of abnormal system events. And this is the main thing we need to know: Abnormal states cause abnormal events. If we correct the abnormal states which are causing our abnormal events, we have solved the problems.

Next, below, is a more scholarly treatment of the same subject, expanded, based on the work of British philosopher John Stuart Mill.


Based On John Staurt Mill's "Methods Of Inductive Inference."
The Formal Logic Of Diagnostics


Universal Troubleshooting Process

Here is a book that Steve Litt recommends to help you find the root cause of any problem, automotive or otherwise.

The Root Cause Analysis Handbook-A...


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Blessings to you. May God help us all.

       Rev. Bill McGinnis, Director -

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