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Avoiding Diagnostic Rabbit Holes


Electrical and electronic faults often pose unique diagnostic challenges in that they seldom present themselves in a clear cut manner that points to an obvious solution. Instead, the symptoms are often contradictory and point in several directions, leading to real diagnostic dilemmas. The consensus is clear that having a diagnostic game plan is of critical importance when facing these challenges, yet because each diagnostic case is different, it is often hard to execute your strategy faithfully. The articles gathered in this month’s feature each touch on ways to stay on track and be more efficient in the ongoing effort to avoid the diagnostic rabbit hole.

Compound Human Error, Part 2

In this very real world case study on diagnostic approach from, Jamie Lazarus dives into a case he was asked to assist on related to a 2009 Chevy Cobalt with an intermittent charging system error light. This one has all the essentials of a classic diagnostic whodoneit: a vehicle with very little known history, an intermittent fault that was hard to reproduce, an obvious previous collision repair, pressure to get the vehicle back to its owner and that little voice that wondered if the root problem was really addressed when the vehicle was released. Of course, the answer to that last component was no. It is a great example that, no matter your experience level, it pays to try to look at the big picture before getting locked in on a specific symptom or potential problem part. “Did you ever get the feeling there was just something you were missing? That there was something you should have picked up on?  These were the feelings I was having when they called me!… It seemed the car was getting “sicker” the longer this went on!” Read the full article here.

PCM at the Center of the Whirlwind

In this article by Gary Gomes from, he keys in on PCM-related diagnostics. This is relevant to no-crank and/or no-start diagnosis, as so often the symptoms on these repairs point back to the PCM or a communication problem related to the PCM. In the article, Goms refers to following “the electronic trail”: “…we’re going to explore how to diagnose many common powertrain control module (PCM)-related drivability and electrical problems by following what I call The Electronic Trail.” He notes that the trailhead (where you start the process) is always the battery. He goes on to identify some common pitfalls in PCM diagnosis, provides a rundown of the mindset needed to successfully resolve these system errors and provides examples of how he uses data provided by the disabled vehicle to pinpoint the source of the problem. It’s a good read. Read the full article here.

Don’t Forget to Check Reference Voltages

In this article from, Dan Marinucci addresses the importance of system components receiving a proper reference signal to enable proper function and illustrates his point with the case of a 2008 Honda CRV with a drivability issue that later turned into a no-start issue. In the case in question, the vehicle was in for service at his friend Lenny’s shop. Lenny pointed out the crux of Marinucci’s point, saying “[He] emphasized that the CR-V job reminded him of the value of basic tests such as checking ref voltage – not to mention doing so early in the diagnosis.” The diagnosis eventually lead to a shorted sensor and more widespread damage, but the no-start stemmed from an inability of the sensor to communicate with the rest of the system. The article does a good job of showing how communication errors and mechanical failure sometimes go hand in hand. Read the full article here.

You are Not Alone

We close with a great reminder that help is just a click away. When you enter the diagnostic rabbit hole, you can sometimes feel like you are all alone wrestling a unique issue, with nowhere to turn for feedback or direction. But this article from Pete Meier on reminds technicians that there are many resources where you can research how other techs resolved similar issues or ask for help if you don’t see an issue covered by a previous poster. “Another valued feature is the Fix database hosted in iATN. This was the accumulated results of every Tech Help message ever sent or answered. Perhaps the problem I was facing had already been faced, and beaten, by another tech? If so, this was the first place to go see.” He notes a variety of resources to help techs resolve troublesome repairs as well as enable them to be more efficient in their diagnostic process. He also adds a word of caution that perhaps some of these strategies are overly simplistic and can cause a tech to load the parts cannon. In the end, he suggests applying each of these tools in a manner that improves efficiency while also ensuring effectiveness. Read the full article here.

With the ever increasing complexity of vehicle systems, particularly the electrical/electronic systems responsible for starting the vehicle, a tech really has his or her work cut out for them. These articles, and the many we have highlighted in the past, emphasize the need to have a clear strategy, possess critical vehicle information about what proper function looks like, never forget to check that the system has proper communication, utilize the right tools for task in front of you and take advantage of the resources available to you online through your information system and forums such as iATN. Doing so will help you, when you are on “the electronic trail,” avoid the rabbit hole most of the time and, in those instances where you fall in, your stay will be brief and less painful.

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