Auto Service World
Feature   March 1, 2000   by Craig Cook

Lose the scope and scan tool – It’s crayons you need for diagnostics

It may seem far-fetched, but a technical trainer advocates the use of crayons for a better understanding of wiring diagrams as a diagnostic tool. If you thought he was from California, you'd be right.

It’s often said that going back to the basics is the best way to handle complex underhood troubleshooting. But if you thought colouring with crayons was going too far, think again.

That’s exactly what happened at an advanced level technical seminar for technicians who wanted to learn more efficient diagnostic strategies.

More than 30 automotive professionals who attended the recent class on how to master wiring diagrams, by Jorge Menchu, learned that the complex can be systematically broken down into simple, logical, easy to understand circuits.

Menchu, a self taught electronics expert from Fresno, California, used the crayons to demonstrate a well thought out, systematic approach in dealing with and understanding the complex electronics found on vehicles today.

Each colour identifies a different voltage and where it exists in the circuit. The beauty of using colour is that it highlights individual circuits and paths in complex wiring diagrams.

Menchu was hired by Ron Brown of Auto Know Inc., to make the day-long presentation at a hotel in Toronto one recent weekend.

In order to master the complex, Menchu said you must first master the basics.

“Regardless of how complex something is, it is nothing more than a bunch of simple elements. Usually the basic elements are a lot easier to understand than the complete system and offer a starting point for growing your knowledge to master the complex,” he said.

A lot of emphasis was placed on the self-learning approach based on the following tenets:

Use the workshop as your classroom;

Learn from every diagnosis

Train yourself to understand the basics

Avoid tunnel vision

Utilize what you know

Learn what you don’t know

These were some of the messages that Jorge — who got chuckles when he jokingly said he earned his degree from the University of Radio Shack — said he was trying to get across to the attentive audience.

All too often you can get lost in the maze of diagnostic trouble charts that the engineers have formulated to try and help you pinpoint any problem that may occur on the vehicle, he said.

Most of the time the problem that you have in your shop doesn’t pertain to the problem that the engineers wrote the diagnostic troubleshooting charts for in the first place.

Wiring diagrams do offer information in the form of text and symbols, he said, stressing the importance of identifying the diagram symbols in order to understand what is actually happening inside the circuit.

The symbols are a high level language that represent the devices that create the circuits that create the systems.

Systematically break the diagram down into sub-systems, he said, then break the sub-systems down into individual circuits.

By doing this Jorge demonstrated how the complex maze of wires and symbols was much easier to understand and follow.

Individual circuits were identified and then the component within the circuit was discussed.

Most fuel injectors have battery voltage applied to one terminal in order for the fuel injector to operate, and it must have a ground circuit supplied to it by the Powertrain Control Module (PCM).

By knowing and understanding the basics, you can determine that, in order for the PCM to turn on the fuel injector, the PCM has to receive some sort of electrical signal, usually a signal from the crankshaft sensor.

Once that signal has been processed by the microprocessor, the computer then signals the transistor to supply a path to ground for the fuel injector.

If you understand how crankshaft sensors and transistors work (transistors are just electronic switches), then you could probably troubleshoot the circuit with nothing more than a wiring diagram (for guidance), a voltmeter or lab scope.

Colour Coding

Jorge has developed his own color coding system to help technicians understand what is supposed to be happening in the system.

The process of color coding is used to identify the different voltage conditions that exist in each part of the circuit. Colours highlight individual circuits and paths for complex wiring diagrams.

Once the component and its operational requirements were understood, packages of crayons were handed out.

Upon receiving these crayons a look of amusement could be seen on the faces of a lot of technicians in attendance.

“If you had to explain to the kids where you had been all day, you could tell them that you had been at a training seminar coloring with crayons,” said Ron Brown.

Using the color coding legend provided by Menchu, the guys coloured in the individual circuits, keeping it simple by first colouring in the power and ground circuits, then applying the colors for expected voltage conditions during circuit operation.

Once the colours were in place, it was amazing to see the simplicity of the circuit.

Following the finished color diagram made it easier to understand the flow of information through the circuit. Then the whole maze of text and symbols suddenly made sense.

Answers seemed to jump right out of the page using the colour method, without the confusion that can occur in your mind as you try to absorb and systematically follow the diagram.

Putting it all together

For the final exercise Jorge worked the class through several diagrams using the color coding method.

Once the exercises were complete Jorge discussed how to create a diagnostic truth table. The purpose of the table is to show the operational characteristics of the circuit under different conditions.

By filling in the different boxes in the chart you can anticipate the expected readings at different points in the circuit.

Jorge also talked about the increasing use of lab scopes that give technicians the ability to see what is going on inside the circuit. ‘With a solid understanding of electricity and electronics, then it is possible for the technician to understand and troubleshoot the problem using his or her own abilities’.

Jorge Menchu operates a company called Automotive Electronic Services (AES) in Fresno, California.

He started AES in 1990 with a focus on diagnostic equipment and training services and as a consultant to the automotive industry.

The company’s main focus is on providing educational products, specialized test equipment and accessories, including the design and manufacture of test leads and equipment.

Anyone with a need for state of the art training, technical information and diagnostic equipment should contact Menchu. If you have Internet access, check out his web site at SSGM

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