The Trouble With Trouble Shooting And Car Diagnostics

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VW Damage from a Rat

Finding damage like this can be rare

We have talked before about the diagnostic process that auto mechanics must follow. Starting with the basics, getting good information and being thorough are vital to repairing cars. There are times however that all the processes and information in the world do not guarantee a proper diagnosis.

Yesterday I spent the about half the day with a QTM working on a car. The QTM is a regional tech that travels to dealers. He deals with new cars, cars that have multiple repairs, and the extra crazy problems. The QTM has a lot more resources than we do at the dealership level. On top of that, these guys are REALLY smart. The kind of folks that will forget more than guys like me will ever know.

The QTM and I were working on a 2013 Jetta Hybrid. The customer’s concern was the car would shut off. It was shutting off differently than it is programmed to. We went round and round with the car, doing test after test, inspection after inspection. All to find NOTHING! Well, not exactly nothing, but nothing final. There was no “Ah Ha, here is the problem” moment. There was a lot of “well, this might be it,” and “it could be the issue”.

Not finding the exact problem is a very common thing. Many times we have to focus on the part that makes the most sense. Or the part that is the least crazy(seriously). So how does an auto mechanic fix your car right the first time? Here are a few things that I use to help narrow down a failed part:\

  • Known good parts.
    The great thing about being at a dealer is the ability to swap parts. Taking a part off a new car to see the change. If a sensor is not reading right and I swap the sensor, I find out if the sensor was good, if the wiring was good, and the module the controls it.
  • Comparable Vehicles
    This is an easier step than actually swapping a part. I can read sensor values from both cars. That will give me an idea of what the car should see. Comparing that to the car with the issue, and using confirm failures.
  • Experience
    This is the biggest and best tool in a mechanic’s tool box. The more problems a mechanic sees, the more they are prepared to deal with new issues. That doesn’t mean a they will not get stuff on problems. It just means they dig through them faster.

Like I said, even with all the proper information, a mechanic doesn’t always know 100% if a repair will be successful. Now if a tire has a big spike in the side of it, we KNOW that is why it is flat. Check engine lights and drive-ability issues are generally not as cut and dry. There are times when we need to roll the dice on a repair. I say it all the time, it is great to be a lucky mechanic.

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Thank you all for the kind words about the new house. Jenn (my wife) and I are really excited. She is even more excited than I am. Fellas you know how important that is! 🙂

10 replies
  1. service plus
    service plus says:

    The main problem usually occurs with the filter just inside the air conditioning unit panel. Most people can change the filter themselves, but they neglect changing their air conditioning filter once a month and it ends up clogging. When the filter gets clogged, the condenser fins on the inside part of the furnace can not “breath” which causes it to freeze up, literally. Be sure to change your filter and try turning the unit off for a few hours to allow any ice to thaw.

  2. Jesse
    Jesse says:

    You’re right, I think experience indeed goes a long way. If you’ve seen the problem before on the same type of car you can easier deduce what’s going on. But I would imagine a 2013 Jetta Hybrid would be harder to fix from experience being extremely new.


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