Vehicle Diagnostic and Troubleshooting Process Revisited

        Hello. I have thought for some time that someone should provide a general and universal vehicle diagnostic process guide. After writing most of this post, I searched the internet for such a guide. I felt sure someone had written a general diagnostic procedure and I not only found one, I found one containing exactly the information I wished to present and written better than anything I could have produced. It is written by Steve Litt and is called “Twenty Eight Tales of Troubleshooting”. Below is the link to the site where the e-book can be purchased. The site outlines the process, but I highly recommend buying the book. It is not a technical manual, but is written more like a collection of short stories. It is an entertaining, easy read, but contains the philosophy of the general troubleshooting process. Anyone who is serious about becoming a better mechanic or is just beginning a career will find it well worth the few dollars it costs. I also believe this information should be part of the curriculum in any repair education program.

                                                           troubleshooters.com

Rather than reiterate the information presented by Litt, this post will add my views on some aspects of the vehicle repair industry that inhibit efficient, timely, and cost effective  repair.
I think the most interesting aspect 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 how decisions are made during the process of vehicle repair. 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”. I am not talking here about the nuts and bolts of the process, not of how to check circuits or to find a failed component in any specific case, but of how to make sound troubleshooting decisions.

        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, and repairing 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.

        Another aspect of communication with the customer arises when a vehicle is brought in with more than one failed component or multiple conditions. It is not uncommon for a customer to continue driving a vehicle that has a driveability or starting problem, and this can cause a problem for the mechanic in diagnosing the problem or in determining the problem’s root cause. An example could be a truck with a long crank-to-start when cold. As long as he can get the truck running, the owner may continue driving it until one day it won’t crank. A mechanic diagnoses and replaces the failed starter, but if he doesn't know about the hard cold start, he won’t address the root cause of the failure and the vehicle will be back again. This specific problem as well as similar ones is a common cause of customer dissatisfaction as well as unnecessary warranty work. Multiple failures of components across time can sometimes lead to baffling troubleshooting sessions and difficulty getting to the root of a problem. The only way to address these problems is getting complete information from the customer at first contact. 

        Mechanics or service writers need to be sure that they know exactly what the customer is experiencing and that the symptom can be reproduced. The customer may need to be prompted by specific questions about what happened and when. The mechanic must be given enough information about the problem and when that problem happens that he can reproduce it and find a solution. This sometimes means that the contact person must ride with the customer to experience firsthand what is going on. The knowledge about the problem that the service writer experienced needs to be put on the work order. If another tech takes the over to complete the job, the first mechanic must provide complete information as to what was done so that no time is wasted by duplication or missing 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 else takes over, he knows what has been done.

        Lack of good or complete diagnostic information is another issue, especially for tough problems. Probably the only time you will ever get anything like complete information is at a dealer working on that dealership’s brand. Of course, much OEM information is available to independent shops, 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. 

In addition to the problems described above, a vehicle engine is made up of several subsystems designed to work together. The mechanical, electrical, electronic, high and low pressure hydraulic, cooling, intake air, and exhaust each play a role in keeping a modern engine running as it should. In contrast, a computer system outside of a network has only two systems, hardware and software. Granted, a software program can be thousands upon thousands of lines of code, but it is still one system. The interconnection between different systems in a vehicle means that a fault in one can cause symptoms in another, often masking the root cause.

        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 a few hundred dollars 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. OEM diagnostic programs are expensive and need periodic updating for late model vehicles, but 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 an OEM program will allow the user to do things like actuate relays, check sensor function, run injector disable tests, and reprogram vehicle modules. Wireless internet access is also very beneficial, especially with OEM laptop software. For these reasons, a shop that owns just a generic scantool limits itself to the most basic diagnostic jobs. 

        Technician knowledge, experience, initiative, and persistence 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 learn new skills. Worse yet, some 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 easier than ever to find needed information, and there should be little excuse for lack of knowledge.  If you work at an independent shop, you have a few years before starting to see new technology show up on the vehicles you service, and tips and other information will become available from aftermarket sources and online. 

        The diagnostic process itself must follow a systematic and logical path in order to arrive at a solution. By systematic I mean that the process has sequential steps in proceeding from a general observation of a problem to increasingly specific tests that narrow the search until the answer is found. Logical means looking only at components having to do with the system in question, and then allowing each step in the process to guide subsequent efforts. In an earlier post I outlined something I call the VEHICLE diagnostic process. It can be used as a very general jumping off point for further refinement. It goes as follows:

The VEHICLE diagnostic process

First - law #1:  Make sure the simple, cheap, easy things are right before moving on!

V: a VISUAL check is the first step.

E: check the EASY things next.

H: HOOK up a scan tool for problems on a system monitored by the ECM.

I: ISOLATE the problem to a smaller area within the system.

C: CHECK each item only once. (unless you changed something)

L: the LAST action is to always verify the repair.

E: EVERY problem has a simple solution.*

*simple doesn’t necessarily mean easy to find. And rarely a problem may have multiple causes. But most difficult problems are simple ones hiding behind layers of distraction

Please check the original post if you want elaboration on each of the steps. Note that this process is systematic and logical, and it is also very similar to Litt’s 10 step process. Incidentally, this post except for this first and this last paragraph were written before I ever came across “Twenty Eight Tales…” Every successful vehicle diagnostician I have ever worked with follows the same basic process in working a problem, so it appears that whether through trial and error or by being taught, we all find pretty much the same set of tools.  

Thanks for reading today, and good luck in your efforts.