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My 2003 Honda Civic EX is experiencing an issue which causes the battery (alternator/charging system) light to occasionally come on for less than a second.

The car starts, runs, and drives fine without any noticeable dimming of lights or odd noises when the battery light flashes. All fuse boxes have been checked and no fuses are blown, damaged, or disconnected.

The voltage for the car once warmed up is roughly:

  • 14.5V when idling (no headlights radio AC or blower fan)
  • 12.15V when idling immediately after headlights, radio, AC, and blower fan are turned on
  • 13.2V when car is shut off after running for a while (key in off position no lights etc.)

These measurements were taken on both the battery itself and the terminal connections and were consistent; there is no visible battery corrosion.

I have read several similar questions on this site; however, none of those situations seems to be quite what I am experiencing with this car.

flickering battery light

battery light flicking on dashboard

This to me is the odd part. The battery light seems to come on when the lights and other accessories are OFF especially when the gas pedal is lightly tapped multiple times, it will flash each time; driving with the headlights ON and fan blowing the light rarely, if ever, seems to appear.

All belts are tightened to the point where they do not squeal or noticeably slip. One wire of the four wires in the harness for the alternator was broken and attached via solder; however, there is no resistance from the solder bead to the harness terminal which connects to alternator.

I would assume that theses momentary flashes of the battery light indicate something which is likely to be potentially hazardous to the longevity of the battery or alternator/charging system.

What is the best strategy to diagnose the problem I am experiencing?

  • Were you able to figure this out? I have somewhat similar problem on my Accord. – tumchaaditya Aug 8 '18 at 15:00
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To eliminate it right off the bat, the problem would not be in the battery itself. The voltage you state for rest (13.2vdc) is right where I'd expect a good battery to reside after running.

This leads me to think of one of several things where the issue may be.

First, it might be a worn belt which is slipping and you aren't noticing it. If the belt is worn enough, it may be skipping over the pulleys in certain spots. A worn serpentine belt is actually hard to diagnose without a tool. Here's an example of one:

enter image description here

It measures the depth of the grooves in the belt. A worn belt could still have the grooves, but they'll be worn and broader, allowing the tool to bottom out, which it shouldn't. Even if you don't have a tool, if your belt is old (over ~50-60k miles for a normal belt - if Kevlar, 100k), replace it as a regular maintenance item.

The second area of concern would be a failing regulator in the alternator. This could be intermittent under the right circumstances, causing the light under just the right circumstances. This second is a long shot, but really if the belt, tensioner, and pulleys are in good shape, this is where I'd go next. You could take your alternator down to most parts shops and get it checked, but it may not show an intermittent charging issue.

You can also check all of your connections and grounds to ensure they are tight, clean, and making good contact. If a wire just happens to get in the right position while the engine is settling after you rev it, loses connection, and the light comes on for a brief moment. Long shot and very hard to diagnose, but it could be done. The easiest what to check for this is to have a helper in the driver's seat, engine running, then you go through and move wires associated with the charging system around a little bit and see if you can get the light to come on. Like I said, a long shot, but about the only other thing you could check. This may take going over all the wires several times to eliminate it as a possibility.

  • I will have to examine the belt for potential wear, I recently installed a new Dayco belt replacing the Bando one which was making noise. The new belt has roughly 3k miles but needed the tension to be adjusted after installation because it too was making quite a noise,unlikely but perhaps in that time it was worn slightly. When adjusting the tension I first noticed the loose wire. I am not sure if I damaged it while tightening the wing nut or it may have even been this way from the previous owner. I am curious if it is the wire which controls the lamp itself I believe one of the four does. – John Dream Mar 31 '17 at 16:16
  • For clarification the battery light showed up only after attempting to adjust the tension several times, not immediately after the new belt was installed. – John Dream Mar 31 '17 at 16:17
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    @JohnDream - If you just replaced the belt, this wouldn't be the issue. Check the connections to the charging circuit (alternator/battery). If nothing pans out there, take the alternator in to see if there's an issue there. – Pᴀᴜʟsᴛᴇʀ2 Mar 31 '17 at 16:43
  • Would a dealership, parts place, or Repair shop be best to examine the alternator? I assume it would still need to be on the car for them to do a proper test – John Dream Mar 31 '17 at 17:04
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    @JohnDream on car is the best way to check the charging system. have a shop or dealer check the whole system for you if you don't have the tools or wiring diagrams for the car. iirc these models are all ecm controlled and use a load detector in the fusebox. it may just come down to a poor connection at your alternator. – Ben Mar 31 '17 at 17:30

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