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The three-legged stool approach to vehicle diagnostics

Monday, October 1, 2018 - 06:00
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With the proper training, the correct tooling and a thorough understanding of how our opponent (the subject vehicle) “ticks,” the odds are high that the fault can be identified, the root-cause pinpointed, and vehicle repaired in a reasonable amount of time. That is, of course if we can identify what the customer is concerned with.

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Lesson #1 – The three-legged stool

I want to take a moment to bring up a very valuable lesson I learned years ago from AutoNerdz founder Tom Roberts. Tom is an invaluable contributor to the automotive industry and is known for his diagnostic and scope expertise. He once described the ability of a technician to perform his/her duties as being perched upon a three-legged stool. The three legs represent a technician’s competency, capable tooling and adequate information.

I believe Tom used the analogy because, just like a three-legged stool missing a leg, a technician who lacks one of the three items would soon find himself toppling over in a crash-landing. We must fortify ourselves from those three angles to be consistent and successful diagnosticians and technicians.

Lesson #2 — The 85/15 rule

There is another valuable lesson that I was taught years ago. About 85 percent of every action that occurs on an automobile, occurs on all of them because it must. It is a matter of physics. For example, we can energize a fuel injector by completing the path to ground, by providing a voltage source or even by providing both a voltage source and ground path. The point is the injector must open to allow a cylinder to be fueled properly. The 85 percent is that very fact…the 15 percent is how the manufacturer designed that function to be carried out. This very lesson is the basis for this topic of discussion.

The initial encounter

The vehicle in question is for a very loyal fleet account of ours (Figure 1). It seems their 2013 GMC Sierra Diesel 6.6L (LML) with 186K on the odometer has been experiencing a loss of coolant level for some time now. I was issued the vehicle for evaluation along with some basic routine maintenance. The vehicle was well maintained and in fine shape. I noticed the degas bottle exhibiting a very low level of coolant and in the engine compartment the unmistakable, sweet smell of hot antifreeze lingered over the hot powerplant. A visual inspection of the hoses was carried out and the leak was easily pinpointed to the lower radiator hose. I received authorization from the fleet manager to complete the repair and the vehicle was ready for pick-up later that same afternoon.

Figure 1
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