Intermittent Battery/Generator Warning Light

[TrishP]

Hello All:
Am back here to pick your brains for my latest vexation.
But first, re my windshield fogging post in January, a shout out to Neil who suggested checking ALL the filters, which, I am embarrassed to say I did not know existed. The cabin filter was a disaster and replacing it remedied my problem 100% )
The current dilemma is this: on Saturday while doing some city driving, in horrific heat, I noticed the AC got a little wonky, and then the battery light would intermittently appear. It seemed to occur upon harder acceleration and rounding corners. As an aside, a guy stopped me during this and asked if I wanted to sell my car )) lol.
Problem continued, so last night I finally located my last battery receipt and it was from 2011. Decided to call AAA and their service tech tested both the battery & alternator and said they were fine. I got a new battery anyway, because, well, it was convenient & seemed timely.
Today, the light did not go on---but am wondering if it possibly WAS the battery OR if because the computer resets, it just hasn't come back yet.
Any thoughts/ideas appreciated.

[BEJinFbk]

The idiot light for the alternator is pretty simple
and doesn’t generally trip any codes in
the OBD2 computer.
May have been a bad battery, a poor cable connection
or possibly the first signs of a charging
system issue. Keep Driving!

[amblerman]

Hello All:

The current dilemma is this: on Saturday while doing some city driving, in horrific heat, I noticed the AC got a little wonky, and then the battery light would intermittently appear. It seemed to occur upon harder acceleration and rounding corners. As an aside, a guy stopped me during this and asked if I wanted to sell my car )) lol.
Problem continued, so last night I finally located my last battery receipt and it was from 2011. Decided to call AAA and their service tech tested both the battery & alternator and said they were fine. I got a new battery anyway, because, well, it was convenient & seemed timely.
Today, the light did not go on---but am wondering if it possibly WAS the battery OR if because the computer resets, it just hasn't come back yet.
Any thoughts/ideas appreciated.

Something very similar happened to me recently. You can read about that in this thread:
viewtopic.php?f=1&t=90163

The battery light (to the best of my knowledge) is not really a light about your battery. Rather it's an indication that your general electrical system is not producing the proper amount of electricity. Or rather, some portion of the system isn't getting or seeing the proper voltage and thus tripping the light. What isn't clear to me is why this is happening if your alternator did check out. There are only three connections on your alternator: ground (bolts holding alternator to engine), positive wire from starter (ie to + post on battery) and a tiny wire which I've been told goes to the light on dash. But I don't understand how or where the system is measuring output of alternator to trip light on dash.

In my particular case, it turned out to be a combination of two things:
a) loose connection at positive battery terminal. The connection from the battery terminal to the fuse box was definitely loose. If this really caused my issue, I can't say for sure because... (see b).
b) the voltage regulator on my alternator proved to be on its way out and my alternator wasn't putting out any voltage.

But you say your alternator and battery are fine and have been checked out. In that case I would look at what a lot of people told me about.

Namely the cable that goes from the battery to your fuse box. If you pop open you fuse box (under hood) it will be the only wire attached with a bolt. These tend to go bad . See this thread for a nice walk through and pictures of heat damaged sires.
viewtopic.php?t=35208

The theory is that they may work fine when your car isn't using a lot of electrical systems. But if you put a lot of load on it (ie AC with fan on high, with lights on, and blasting your radio so you can hear it over the AC.....) then you are putting extra load on the system and the wire from your battery to fuse box won't be able to take the extra load and the resistance will go up which decreases voltage which trips the light..... But again. I don't fully understand what can trip the light. I Just know that if the cable from battery to fuse box is wonky (great word btw) or loose, it can make all sorts of bad things happen.

At least that is my understanding.. I am sure there are people on here that could do a better job of explaining it or correct me where I went wrong.

[Ozark Lee]

I had a similar intermittent issue on my Platinum Edition and it took me forever to find the problem. In my case the wiring harness rubbed against the amplifier for the stereo which has really sharp cooling fins and rubbed a hole in the insulation and shorted it to chassis ground.

The battery was fine, the alternator was fine but the indicator light was always lit. After hours tracing the wire the fix took about 5 minutes.

...Lee

[Herb Goltz]

I have had intermittent charging lights when the alternator brushes were worn-- they seem to wear asymmetrically and occasionally they make poor contact with the armature and you get the dash light. Because of the intermittent nature of the problem, this can be difficult to diagnose. Charging issues are a problem in really cold and really hot weather. You may need a voltage regulator/brush assembly soon. I have replaced the assembly with the alternator in the car-- kind of a nuisance, but less work than removing the whole alternator.

Good luck!

[amblerman]

I have had intermittent charging lights when the alternator brushes were worn-- they seem to wear asymmetrically and occasionally they make poor contact with the armature and you get the dash light. Because of the intermittent nature of the problem, this can be difficult to diagnose. Charging issues are a problem in really cold and really hot weather. You may need a voltage regulator/brush assembly soon. I have replaced the assembly with the alternator in the car-- kind of a nuisance, but less work than removing the whole alternator.

Good luck!

I would caution anyone doing this to watch out for two things.
1) you have already disconnected the positive and negative terminals at the battery. Not just negative terminal. If you only disconnect the negative, you'll have a hot/live positive terminal right in the middle of your alternator that you'll be working around.

2) be very careful of any Phillips head screws you may have to take off. The ones on mine seemed to be made of something slightly firmer than chilled butter and I stripped them almost immediately. I think this would be even easier to do when trying to remove them at an odd angle if doing it in the car.

But I agree it could be done. Just tricky.

-A