Hello. I have thought for some time that someone should provide a general mechanical diagnostic guide. Although writing a comprehensive process for all troubleshooting tasks would be a daunting task, I think it would be a valuable tool for beginning mechanics and a good mental exercise. I have doubts as to my ability to adequately provide such a resource, but I will use this forum as a jumping-off point.
I think one of the most interesting aspects of the vehicle repair industry is diagnostics. Many laypeople believe that diagnostics is merely reading codes off a computer and changing a part. Some see mechanics as “grease monkeys” or glorified parts changers. We in the industry know otherwise, but realizing the full importance of good diagnostic procedures doesn’t develop until we have been around awhile and have seen mistakes made and money and time wasted. I am particularly interested in the diagnostic process and how decisions are made during that process. It seems as if good diagnosticians are born with or develop the ability to a high degree, while others just don’t seem to “get it”. Not having gone through formal mechanic training myself, I don’t know firsthand how much diagnostic theory is taught in school, but judging from curriculum I have seen, little effort is made. I acknowledge that it would be a very difficult subject to teach and I have never seen any books on the subject, but it seems to me that any effort made in this direction would benefit all involved. In the Nanoscience Technology program from which I have my degree, we had a class in Design of Experiments, or D.O.E. This focused on optimizing, analyzing, or fixing systems of deposition or removal of materials onto silicon wafers. The process chamber pressure, gas blend, temperature, and time are systematically varied and the result of each recipe is measured. In this way an optimal process is arrived at or a problem identified. This type of analysis doesn’t really apply to the vehicle repair situation, but what does apply is that diagnostics can be taught and that a procedure and careful documentation should be part of the diagnostic effort.
Several challenges exist which make vehicle diagnosis a unique situation. Communication problems often exist between customer and service writer, between service writer and mechanic, and when another tech takes over the job or if the vehicle comes back again. Lack of good troubleshooting information, and gaps or incompleteness in that information also contribute to difficulty in making an expedient repair. Inadequate or obsolete equipment or instruments often exist in even well-equipped shops. Lastly, technician inexperience, lack of training, or outright laziness have always been problems.
One contributor to the communication problem is the lack of a common language between the customer and shop personnel. Technicians tend to be very specific with the words used to describe an unusual noise, for instance. A squeak is different from a squeal or a whistle, and a tapping noise is different than a knock or a rattle. Customers however, sometimes use some of these terms interchangeably or with different meanings. Mechanics or service writers need to be sure that they know exactly what the customer is experiencing and that the symptom can be reproduced. This sometimes means that the contact person must ride with the customer to experience firsthand what is going on. Another communication problem is that the mechanic is sometimes not given complete information on the exact nature of the problem or complaint. The knowledge about the problem that the service writer has needs to be put on the work order. If another tech takes the over to complete the job, the first must provide complete information so that no time is wasted by duplication or missed information. Complete communication, preferably in written form, must be provided by all parties involved. If I print a diagnostic procedure from an information source, I like to check off each step and write down any meter readings or measurements I get from doing that step. That way I keep track of where I am if I take a break and if someone takes over, he knows what has been done.
Lack of good or complete diagnostic information is another problem, especially for tough problems. Probably the only time you will ever get complete information is at a dealer working on that dealership’s brand. Of course, OEM information is available, but the cost tends to be high for independent shops, so many of us don’t have access to it. Non-OEM sources, in my experience, can contain spotty, incomplete, or even false information. Of course, anything is better than nothing, but no matter what the source, you must be able to think for yourself and watch for something that doesn’t make sense. You also must know enough about the system you are working on to be able to fill the information gaps a source might have and in some cases to solve a diagnostic problem without any formal information.
Nearly every diagnostic process will require some kind of equipment or instrument, and you will need to provide at least some of it yourself. I would say every mechanic needs, at minimum: a good digital multimeter, a set of backprobe pins or leads, a dial indicator, a caliper or micrometer, and some kind of gauge for air and fluid pressure checks. These are pieces of equipment that a shop may not provide due to the difficulty of keeping them in good working order when they are used by everybody. The cost of all these items really isn’t that great, especially when compared to the many sockets, wrenches, and other hand tools most mechanics own. If you spent just $500 on this group of tools, you would be getting quality products that would last for many years, if not the rest of your career. Of course, the cost of diagnostic laptops or scanners is beyond the reach of most mechanics, and any repair shop that wants to repair vehicles will have one. A scanner to read codes and display a generic datastream would be the bare minimum. Laptop diagnostic programs are expensive and need periodic updating for late model vehicles, but usually have more capabilities than a simple scanner. Most shops should have both, as a scantool is good for quick checks of a system or for use on the road, whereas a laptop program may allow the user to do things like actuate relays, run sensor checks, and reprogram vehicle modules. Wireless internet access is also very beneficial, especially with some OEM software. For these reasons, a shop that owns just a scantool limits itself to the most basic diagnostic jobs.
Technician knowledge, experience, and initiative are the most important factors allowing efficient and profitable diagnostic work. Without them, the best equipment and information is all but wasted. Trouble is, many mechanics don’t seem to take the initiative to keep themselves up to date and learning new skills. Worse yet, many of us don’t have the basic knowledge needed for effective diagnostic work. I am always shocked when a seasoned mechanic doesn’t know how electrical relays work or how variable sensors provide information to a control module. In addition to being compulsory, most dealer training is thorough and in-depth, but most independent shop mechanics need to upgrade their skills themselves. In this internet age, it is very easy to find any information needed, and there should be no excuse for lack of knowledge.
I will post more on this subject as new parts are written. Bruce
