The perplexity of electrical diagnostics

Basic principles of general fundamentals avoids confusion


I had a “gee whiz” moment about six months ago in Texas while answering a question in my Fundamental Electrical Troubleshooting class. A student - a highly experienced truck technician - was wondering why all vehicle manufacturers seem to approach the process of diagnosing electrical problems so differently. His exact words were: “You try so hard to make it all seem so simple. Why do the manufacturers seem to work so hard to make it difficult?”

The class took up the issue, and I was really surprised at how passionate the 12 students were in discussing this matter. It was during this conversation that I had a simple thought that at first confused me, but now annoys me.

If you ask 100 technicians to write down the process involved in jacking a truck to change a tire, you’ll get 100 answers, and all of them will be pretty much identical, excluding personal technique. If you ask those same 100 technicians to write down the process of diagnosing a no-start condition, you’ll probably get only 60 answers, and most of them would be different.

This really is a confusing state of affairs. What I have been teaching for the last nine years is this: (a) There are only three faults that can occur in a single wire, and none of them can be confused with another; (b) There are only four types of circuits; and (c) There are only five voltmeter readings, and all of them point directly to the specific aforementioned points.

It really is this simple, and there is no reason for this process to be so difficult. There is no reason for technicians to feel intimidated or foolish when trying to fix a modern truck’s electrical system. There’s no reason for the process to be so disjointed, so scattered, and if you’ll allow this, so schizophrenic.

This brings to mind an anecdote a trainer from a major truck engine manufacturer used during a presentation to engine engineers. He told the group laughingly that his company had developed a new sensor. To save money, that sensor was capable of being used on five different engines. The engineers responded by writing five completely different diagnostic procedures for this one sensor. I laughed at the time, but I’m not laughing now.

All electrical diagnostics revolves around five basic ideas, and I’m completely convinced that if a person fully understands these concepts, he (or she) will be able to fix anything. That been my reality for the past decade while teaching people how to do it.

These five basic concepts are: Ohm’s law - the concept, not the math; Kirchoff’s Law - the voltage drop law; schematic reading - there is a right and wrong way to read them; meter reading - you’d be surprised at what you’re missing; and basic component function - you’d be amazed at how many people don’t know what a relay does.

Another critical consideration has to be the psychological and social environment that exists in every shop across the nation. Having been in shops from Maine to California, North Dakota to south Texas, I can say without hesitation that the single most destructive behavior is the ego-driven harassment that most technicians experience when trying to do things the right way.

It’s my contention that electrical diagnostics and repair is completely reversed from mechanical diagnostics and repair. Diagnosing the average mechanical problem takes minutes, and a confident decision for how to proceed is almost automatic. The repair can take hours, during which the noise, the sparks and the cursing make it clear that the technician is earning his keep. The outcome is time-predictable, and the customer can be given a reasonable estimate of the cost and duration.

An electrical problem is completely different. The diagnosis can take hours, and I can promise you that in the end, the actual tool usage repair will likely take minutes.

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