How to troubleshoot Intermittent Battery Light Issue in 2003 Honda Civic?

Question

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?

Pᴀᴜʟsᴛᴇʀ2 · Answer

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:

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.

Old timer Pete · Answer

One time I had the same problem. The fault was in a pulley that had bad bearings. I replaced the pulley. Problem fixed.

How to troubleshoot Intermittent Battery Light Issue in 2003 Honda Civic?

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