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Go Beyond the Alternator or Starter for Successful Diagnosis


Today’s vehicle electrical systems are complex, even on conventional ICE vehicles, and that complexity can lead to all kinds of issues for vehicle operation and, in turn, technicians. In this month’s feature article, we review some recently published resources related to electrical system diagnosis, with a focus on our old friends the charging system (alternator and more) and the starter.

Based on the frequency with which the trade publications address diagnostics and troubleshooting related to the electrical system, it is clear that this area of vehicle repair is one that is virtually limitless in terms of difficult challenges, model year after model year. Our goal with these survey articles is to collect and present some of the latest thinking on a topic in the hopes that, by doing the legwork for you, we save you the research time as well as present you with resources to make your tasks easier and more profitable. So, let’s dig in.

The State of Today’s Charging Systems

We’ll start with a big one. This article is relatively long, but also packed with great information and insight, which is what we’ve come to expect from Jeff Taylor at In this comprehensive article, titled Maintaining the Vehicle’s Charging System, he reviews electrical system design, its purpose, the ways these systems have evolved in recent years, identifies common system failures and identifies the tools that can simplify charging system diagnosis and repair. As he points out, these issues span all vehicle types: “Even hybrid and fully electric vehicles have a low voltage system, and that low voltage electrical system will control most of the vehicle’s operational systems. Like the ICE-equipped vehicle, these also have a low voltage battery that needs to be charged allowing for ‘ready mode’ operation.”

A key change that he highlights in these systems is the increased output of modern alternators, noting that the 2020 Ram Diesel features a 250A alternator. That’s a lot of power. The biggest change highlighted, though, is one we have emphasized before. That’s the adoption by virtually every OEM of “smart” charging systems that vary charging output and other behaviors based on a large number of inputs, including specific system design, vehicle loads, battery state of charge, temperature and more. As he notes, these smart systems are designed to save fuel consumption and improve fuel economy. We would also say that they are critical for battery longevity – without smart systems to balance loads and give the battery exactly what it needs when it needs it, with the massive electrical loads placing a burden on today’s electrical systems, we’d all be changing our batteries every year.

He goes on to discuss how hybrids and EVs use a DC-DC converter instead of an alternator. He identifies common issues with these systems, similar to how he did with conventional designs. He also reviews the tools needed for system diagnosis, including the carbon pile tester. “Another common tool that is going to be needed to inspect a DC-to-DC converter charging issue is the carbon pile tester. The carbon pile tester is the preferred method to test the low voltage system output of the DC-to-DC converter. Watching the low voltage system’s output while applying a load with the carbon pile tester should indicate an increase in the system’s target current level.“

This article is a great intro to this topic and, we believe, well worth the read.

Alternator Checklist

Our next item is less an article and more of a hitlist of things to think about when it comes to alternator diagnosis and troubleshooting. As Andrew Markel points out in this article on, often technicians see weird or unexpected output by the alternator and immediately condemn it, without digging deeper to make sure the root cause isn’t elsewhere. So, here he runs down things to look for when you see a no charge condition or other examples of unexpected charging system output.

He starts by pointing out that alternator output can vary greatly by make and model, as well as based upon system factors, as noted earlier in this article. He also discusses how alternator control can be managed in a variety of ways, based on system design. He then runs down the many different variables that can impact alternator function and disrupt proper operation, noting that resolving the underlying problem can often change the alternator’s performance from suspect to normal. The laundry list is too long to recap here, but items he includes on his checklist include looking for improper grounds, watching out for installed aftermarket devices, verifying proper communication to the alternator and voltage drop testing all wiring between the alternator and the battery.

It is a great fast-hit checklist that is worth a bookmark and just might prove useful the next time you are in the middle of an electrical system diagnostic nightmare.

Advanced Starter Diagnostics

For this, we turn once again to our old friend Pete Meier from Motor Age and In this detailed article, Pete breaks down how he went about diagnosing a 2021 Chevrolet Silverado LT 4WD 5.3L Trail Boss Z71 showing an intermittent dash message of “Battery Low – Start Vehicle.” After a quick note about how he approaches charging customers for diagnostic work, he digs right in and walks the reader through his diagnostic process, which involves the use of a digital battery tester, an inductive high amp clamp and an oscilloscope.

His first step is to check for obvious problems, such as poor battery connections, evidence of a compromised battery such as battery acid on the terminals and a battery test to confirm proper battery health. After confirming that everything checks out from his initial, basic walkthrough, he moves on to his scope routine.

He then runs through his diagnostic process, explaining the basics or scope usage and providing a quick reminder of how Ohm’s Law comes into play here. He then provides visuals of his scope captures from the Silverado testing and shows how zooming in on the scope’s timescale can help to get more detailed information as to what is actually taking place. He then explains what is seen and how he uses this information to form his diagnosis and then work with the customer on a resolution.

How About a Starter Checklist?

Earlier, we saw a piece by Andrew Markel that ran down all the things that could impact charging system function. As he noted, it is best not to condemn an alternator before making sure that the underlying cause of the vehicle’s issue wasn’t another component or issue impacting alternator behavior. But, what about the starter? Same issues? You bet.

Although it’s quite a bit shorter, this article on is like a companion piece to the above charging system checklist. Just as with alternators, Markel warns that starters are sometimes replaced mistakenly, since there are often underlying issues that prevent proper starter operation. His checklist includes checking all inputs, reviewing the wiring diagram, tips for voltage drop testing and more. Like the charging system piece, this is a great one to bookmark for future reference.

Don’t Sleep on the Modules

Finally, we’ll wrap with a bit of a curveball in terms of what has been discussed so far. In this quick case study on, they break down the diagnostic routine for a no-start/does not crank concern on a 2009 GMC Arcadia. In this instance, the technician encountered a repeatedly blown ECM1 fuse. In this case, the diagnostic path ultimately led to a shorted ECM, but it was only replaced after confirming it was the true source of a problem.

Have you ever encountered a situation where at first blush it looked like you were dealing with a problem alternator or starter, but further analysis drove the diagnosis to a deeper underlying issue? We’d love to hear about it, as would your fellow readers. Please share your experience in the comments below.

2 Responses

  1. I have difficulty changing a windshield wiper! No, this is not meant to be a joke.
    sentry out of 20 start attemps. one leave the motor dead in the water. no cranking.Dead silemce.Battery strength is Good, a scope test reveals.Couldit be an alternator or starter.(starter put in by Honda themselves) 2014 Honda Accord 2.4L with 155 000 miles.

    1. Mark – Thanks for your comment. Honestly, it would be very difficult to hazard a guess as to what is causing the problem. For sure, it could be the alternator, but also could be another issue. We’d recommend taking it to a professional for a diagnostic analysis. Thanks, Jim from Clore Automotive

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