Those Darned Intermittents

The use of electronics in vehicles since the early 1980s has given us cleaner running and better performing vehicles that can go longer between tune-ups and engines that last longer than their predecessors with proper maintenance.

But the more complex a system, the more likely it will fail sometime.

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Many times these failures manifest themselves one moment and are gone the next. They may show up in the car not starting at times or stalling at the most inopportune time. Maybe it will surge or turn on the infamous "check engine" light one day and run well the next. We call these "intermittents".

Imagine your home computer being subjected to temperatures below freezing to over 200 degrees and the constant shaking your automobile electronics receive while driving down the road. These kind of conditions can create small breaks in internal electronic circuits that will cause components to behave as if they have small switches in them that turn on and off at will.

Corrosion from condensation and rapid temperature changes can play havoc with connections also.

This kind of problem is very frustrating for the owner and the auto technician who tries to solve it. The owner wants a dependable car that gets from point A to B without interruption and the technician wants to fix the car and make a happy customer but cannot diagnose the problem if it doesn't occur while doing the testing. The technician also has to weigh the chances of finding the problem by spending an hour or two of diagnostic time on a car that is behaving just fine.

If you're plagued with a problem that comes and goes; before taking it to the shop, log down the conditions when it happens and see if you can come up with a pattern of what triggers the particular problem. Maybe there is no pattern, but if there is, your technician stands a much better chance of zeroing in on your intermittent condition much faster with that information. Some of these problems only happen once or twice a month, which can mean a lot of detective work to try and solve and requires a lot of patience on both sides.

We often have cars dropped off with complaints about a problem we can't duplicate and therefore not diagnose, only to find out later that the problem only happens after driving over 100 miles, or only at first start of the day, or maybe only once or twice a week. The better the information you can give to your service advisor as to when it happens, the more time saved diagnosing the problem which equals money saved on the cost of diagnosing.

The following information is helpful when diagnosing intermittent problems:

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  • All symptoms or problems that have occurred.
  • When do the symptoms present them self? (Morning, afternoon, night, various, only on second start up of the day, wet or dry weather, etc.)
  • Was the vehicle hot or cold, just started, what was the outside temperature?
  • When symptom is present, were you driving or stopped?
  • How fast were you going?
  • How long had you been driving that day? (Long trip, short trip, stop and go driving, driving a lot of small trips, etc.)