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Old 11-16-2009, 11:33 AM   #1
mz3madmax
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Default Intermittent Battery Light

06 Mz3 with 75K miles. I got right at 3 years on the factory battery which is the longest I've had a battery last in 25 years living in South Florida. I learned long ago that the cheap Walmart/Costco batteries last the same as the expensive DieHard and others so I have been using these for a long time and getting more than half of them replaced free (under warranty).

This time, I decided, as a kind of experiment, to go with an Optima Red Top just to see if there was any difference. I've had the Optima in for just over one year now.

Yesterday, the battery light came on - first time I've ever seen it. I checked the voltage on the battery with the car not running and measured 12.7 volts (not bad really). The charging voltage at idle with the battery light on was 13.4 volts (maybe a little low but not too bad).

So I loosened the terminals, cleaned them (they were not dirty at all), and tightened them back - no light for the rest of the day. Then, this morning, the light was back on. I noticed that it went out when I pulled up to a stop light a couple of times but immediately went back on as soon as I hit the gas. Then after about 10 miles on the freeway, it went out again and stayed off.

At this point I'm thinking that it is probably not the battery. I recently replaced the upper motor mount and a sensor in the transmission so I've been digging around in the engine bay a bit - maybe there is a loose wire? I guess the other possibility is that it might be the alternator/regulator going bad. However, they usually fail hard, not intermittent like this.

Anyone have this problem? Any opinions?
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Old 11-17-2009, 12:22 PM   #2
mz3madmax
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Default Re: Intermittent Battery Light

No one ever see this ???

So now I've pretty much got it down to this. When the car sits for 4 hours or more, the battery light comes on when it is first started (about 10 sec after it starts). Then, it goes out after driving about 10-15 minutes and never comes back on until the car has been off for a while. After driving the car, I can turn it off and re-start it 10 times and not get a battery light. Only when it has sat for a number of hours.

First thing this morning, before I started it, I measured the battery voltage and got 12.7 volts. So there is nothing draining it. It starts fine anyway so I don't think that it is the battery.

I checked all of the wiring and connectors that I could get to under the hood and nothing was obviously loose or shorted. At this point I'm starting to think that it could be the alternator/regulator but the symptoms don't add up...
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Old 11-18-2009, 12:51 AM   #3
mz3madmax
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Default Re: Intermittent Battery Light

I've now got to where I can replicate this problem at will. If I let the engine cool down for 2-3 hours or lift the hood for an hour or so, the Battery Light (Mazda calls it the "Charging System Warning Light&quot will light up 10 seconds after the car is started. If I drive it for 10-15 minutes, it then goes out and does not come back on. A few times it would go out and immediately come back on before the 10 minutes were up but it will always go out for good at 10-15 minutes.

I actually replaced the battery with a known good one and the problem was still there so I have ruled out the battery. Tonight, I went through every single connector and wire that I could touch. I disconnected all the connectors and sprayed most of them with DeOxIt connector cleaner, blew them out with compressed air, and reconnected them.

I started the car up and the Warning Light came on. I had checked the voltage on the battery before starting and it was 12.7 volts. With the car at idle and the warning light on, the battery was now 12.2 volts - Not Charging. So I then had my son rev the engine up to 2000-2500 rpm and the voltage stayed at 12.2 volts. This thing is definitely not charging when the light is on.

So I took it out for a drive and after 12 minutes, the light went out. I brought it back home and measured 13.4 volts at idle and 13.9 at 2500 rpm. It was charging now.

Then I shut it off, disconnected the negative terminal, and checked the continuity of the cable running from the generator/alternator to the positive lead of the battery. The cable was fine - 0 ohms.

There is a gray/tan block right at the battery between this generator cable and the terminal. I'm not totally sure what this is. It doesn't show up in any of the on-line service manuals. I guess it could be some sort of protection device - maybe a diode, a fuse, or breaker ?

Does anyone know what this is ???

After the car was warm and the light was out, I measured continuity across this device. I will check it again when it is cold. Otherwise, at this point, the clues seem to be pointing to the generator/alternator and some sort of thermal issue.
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Old 11-18-2009, 05:59 AM   #4
wildcard50
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Default Re: Intermittent Battery Light

if the battery is holding a charge then most likely you are dealing with a alternator problem,i had the same problem on my old honda civic a couple of years ago
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Old 11-18-2009, 03:37 PM   #5
mz3madmax
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Default Re: Intermittent Battery Light

I agree. I spent some time again this morning with the car cold and when the light is on, it is definitely not charging - voltage across the battery terminals at 12.2V. As soon as the light goes off I read 13.8V on the battery.

I'm just really puzzled as to what is causing this behavior. It is so consistent that I have to question if it is the computer (PCM) doing it.

I can find nothing in this circuit that would allow the PCM to control whether or not the alternator is charging the battery though. The only connections to the alternator is a current sensor that apparently lets the PCM determine if the alternator is working or not - no control.

So, the only thing left to do is to replace the alternator/generator. I picked one up on the way to work this morning and I plan to put it in this evening. It looks like a pretty easy job. The only concern I have is that I would like to replace the serpentine belt (which is usually easy) but the AC belt is in the way (which looks very hard since there is no tensioner). I may just do the alternator and do both belts later.

I hope that it fixes the problem (fingers crossed...).
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Old 11-18-2009, 06:08 PM   #6
rpn453
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Default Re: Intermittent Battery Light

It does sound like an alternator problem; probably the internal voltage regulator. It's very unlikely that a battery problem would cause a low voltage light while the car is running, and if it can start the start the car, I'd say it's good enough to rule out the battery as the cause.
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Old 11-19-2009, 12:50 AM   #7
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Default Re: Intermittent Battery Light

OK another update. I replaced the alternator/generator this evening and it seems to have fixed the problem. It was very easy to replace from underneath (one bolt from the top). The only issue I had was that the 12v output connector (black plastic with the cover for the big wire) was different on the new alternator so I just swapped it with the connector from the old one.

Unfortunately, the threads on the new alternator's mounting stud for the connector were stripped. Whoever put this together at the "Re-manufacturer" tightened it down too much and spun the threads off. It was too late to return it and get another alternator from the store (there weren't any more in town anyway) so I ran down to Harbor Freight and picked up a METRIC tap and die set for $12. I threaded the stud M5x0.8 and put a new nut with a washer and lockwasher on it. I didn't tighten it as much as I would like but I think that it will be fine. This worked great - no problems except it added nearly 2 hours to the 45 minute job since I had to remove the new alternator again to fix the stud and all the running around.

But, when I finally started the car, there was no Warning Light. I measured the voltage on the battery at 14 volts - both at idle and 2500rpm with no accessories on. I drove the car about 10 miles (nearly 20 min) and had no problems at all. When I got back home, I turned on the lights, radio, rear window defogger, and AC. At idle the battery measured 13.2 volts and at 2500rpm it measured 13.9 volts. I think that this fixed the problem.

Again, I want to give it a couple of weeks before I declare final victory but it is looking good so far.
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Old 05-16-2010, 12:22 AM   #8
matuszak3
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Default Re: Intermittent Battery Light

Hello, I just read your post and it seems I'm experiencing the same problem. I just rolled up on 100k miles and my charging system is periodically flashing on and off while I'm driving. My light doesn't come on like clockwork like yours was, but I am guessing that I have the same problem with my alternator. I'm reading 13.9 volts while idling and it's passing all tests that autozone is putting it through. I just wanted to clarify with you before I replace my alternator that it DID fix your problem. Any response would be great. Thanks. - Adam
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Old 08-25-2010, 07:07 PM   #9
iyilmaz
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Default Re: Intermittent Battery Light

Hello
I have the same problem, I change battery airtake filter and amp cable, light still turn on when I start the car. So problem is the alternator!?
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Old 12-17-2010, 01:13 PM   #10
dpacker
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Default Re: Intermittent Battery Light

i had the same problems with my new alternator and new battery not charging my battery. apparently my awesome brother didn't plug in a connector all the way till it clicked. thanks for the help bro!
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