Intermittent Auto Warning Lights + Misfires – Not As Easy As 1, 2, 3…

by | Mar 15, 2018 | Car Problems & Repairs

Intermittent Warning Lights Plus Engine Misfires - Not as Easy as 1 2 3Solving intermittent car problems can be challenging for both the customer and the auto mechanic. A new customer came into BA Auto Care and described this series of problems:

  • The check engine warning light came on intermittently.
  • The transmission warning light came on intermittently.
  • The engine misfired in cold weather.

We documented the problems on the job ticket, talked to the customer about how we would approach the diagnostic work, and provided an approximate cost.

Our next step was to road test the car. As often happens with intermittent issues, we were unable to reproduce the issues.  No misfires occurred and no warning lights came on. 

Fortunately, the computer system had stored the information, and we found out that when the car was cold, the engine misfired. We began the diagnostic work by checking “the basics.” The technician discovered that the spark plug access holes were full of oil and that the oil had contaminated the spark plug connectors on the coils. So, our next step was to stop the oil leak.

We replaced the valve cover gasket and installed the plugs with new coils. The technician also suspected a carbon issue so we added a product to the gas tank designed to clean out carbon. Finally, we road tested the car. Everything seemed to be working as it should be. There were no engine misfires or warning lights, but of course, with the problems occurring only when the engine was cold, we could not be 100% sure. Additionally, the computer monitoring system gets the final say as to whether the problem is fixed.  Based on its readings, we would be able to tell if the issue had been resolved.  Unfortunately, it takes about two weeks for the computer system to run all the monitors, so we would have to send the customer off not knowing if the issues had been fixed.

Unfortunately, this time, the problems were back within a few days.

This is frustrating for the customer and the technician, but it’s important to stick with the process and cover the “basics first” before moving on to more complex computer problems. To help the customer feel more comfortable with the process, we showed him the data, and he could see there was still a fuel issue when the engine was cold.

So, where to next?

Well, the car had about 200,000 miles on it so it could be a carbon problem or a fuel injector problem. Trying to find a fuel injector problem can be difficult because there are six of them and you have to figure out which one is causing the problem! We were able to pin down the issue to the right-hand bank of injectors. But the “back to basics” next step is to address the carbon issue first.  To do accomplish this we used a special spray and a cleaner.  We added both to the gas tank. The customer was then instructed to drive until the gas tank was empty and we would recheck the data at that point.

This is where we are now in the process. Diagnostic work can be complex, time-consuming and drawn out, but it’s important to allow the auto service facility to go through a logical process. That’s really the only way to get bottom of the problem, not miss something, and not incur any extra, unneeded expenses — by following a series of basic steps.

Here is a 1 2 3 checklist you can use as a reminder of the steps that a proficient auto shop goes through, in partnership with the customer, to solve an issue — particularly an intermittent one.

#1:  Document the issue or issues. Don’t assume they are related. Fill out a diagnostic form for each issue. You can fill out and print one here.

#2: Don’t forget the problem may be related to the basics. One survey found that 65% of electrical issues were found to be related to the battery and or the connections.

#3. With intermittent issues like the one in this example, be prepared to go one step at a time.

We hope this helps you to understand the process of diagnosing an intermittent automotive repair issue as well as why it might take several visits to your auto shop to root out the problem. Also, you have to realize, you may be dealing with more than one problem.

If you have questions about a problem you are experiencing, you can ask us about it at Auto Answers 4U.


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About the Author

About Brian England

Brian England, the current president of BA Auto Care (formerly British American Auto Care), got his start with an auto apprenticeship in a small town in northwest of London. He came to the U.S. in 1972 to work for a Land Rover dealer in Rockville, MD. A few years later, he started British American Auto Care with his wife, Jennifer. Brian is a big believe in preventative maintenance, and his philosophy is to encourage and educate drivers on the benefits of a regular maintenance plan.