Every shop does this. Diagnosis. But, what is it really? Lots has change in the last 30 years. Some Technicians have kept up, some have not. Some shops invest in training, some don't. Design, and engineering has added an enormous level of complication, all to give you, the driver, and the Federal government what you want and need.
What are the common beliefs about diagnosis?
Feel, instinct, touch and sense. Common issues failure? Sure.
Plug in a scan tool, replace part?
Youtube, allegory, your neighbors last experience?
Really, if your in a modern, professional shop, that is not the list.
To get the real picture of diagnosis, let's start at the beginning. The engineering, build and design. On a modern car, or truck, there are at least 30 modules, and some have well more that 100. There are over 12 communication protocols. Even the simplest system on a modern car is attached to a module. In this manner, what we do for diagnosis, becomes a layered approach. Is it physical? Is it bad data? does a module function as designed. Inputs, outputs, powers, grounds, sensors. It all matters.
So, what to do? Diagnosing means something has gone wrong. from a simple dash light, to a real issue, that shuts you down. With the advent of these layered systems, we now have to deal many times with What we call Cascading Failure. One thing leads to another. Causing multiple failures. Finding the root cause cane require a cascading repair. Especially on GDI, and Diesel. A neglected tune up problem, can lead to a plugged EGR, or Catalytic Convertor. Some of these problems cannot be tested until the early problems are resolved.
So, how do we, at Master Tech do this?
Basics, Basics, Basics.......
That is where we start. We call it Baselining. For example, if your have a bad battery, and there are comm codes, missing data, performance issues, we must be sure the battery, and electrical system is correct. This is before we do any further diagnostics. Sometimes, it is that simple. If not, we then know, the car is not lying to us. On many vehicles, a low state of charge, can take down, and destroy an expensive module. Once baseline is confirmed, the we can continue with a layered approach. Codes, data, test drive, physical inspection, research, TSB's, Recalls. All are a part of this. When the initial diagnosis process is done, we can many times make a recommendation, for a service, or repair. Remember, this is a layered approach. At times, the initial diagnosis leads us to deeper inspection, and testing. We then move to Scope and Pinpoint testing. In the image above, this is a part of that. you may look at this test, and not know from Adam what to do. But, our testing and interpretation says you need a fuel pump. It is electrically failing. This takes a good scope, and attachments. (We have over $100K in our setup) If we do not do the Scope and Pinpoint testing, it would force us to guess. We don't guess. After initial diagnosis, we may also need to take something apart, and look at it. This is real work, and yes, we charge for this. But, our approach to diagnostics is, we don't take anything apart until we know what is wrong. This can be applied 95% of the time.
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