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Intermittent Battery Light

60K views 25 replies 15 participants last post by  fireguy132 
#1 ·
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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#2 ·
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...
 
#3 ·
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") 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.
 
#5 ·
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...).
 
#6 ·
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.
 
#7 ·
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.
 
#8 ·
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
 
#11 ·
HI MZ3 MAdMAx,

I have exactly same problem, took the car to the Service center and diagnose it and they said it is the PCM , Im having 2nd thought since the Brand new price they quote is $1600 and there is no available stock.
Im planning to change the alternator first just like you did but Hows your car after you changed it does the problem did not comeback.

Thanks
 
#12 ·
looks like I am having the same problem with my 05 mz3 sounds almost to a t what yours was doing except mine wouldn't flicker on and off at a stop light. just stayed on for about 15-20 minutes then it started charging. sounds to me like some kind of thermal problem. my biggest issue right now is getting the plug off of the alternator. as for the belt I thought the same as you I'll replace it while I'm in there but ya the AC belt is in the way!!!!! how do you release tension on the AC belt to replace the alternator belt?????
 
#17 ·
This is going to sound slightly bizzerk but I had a first gen with this problem. Ended up being the maff wiring harness was damaged from the intake
 
#23 ·
OK, new update...

The car had been running fine since Nov 2009 with no issues. Then almost exactly one year ago (late Jan 2013), the same alternator problem popped up again. My daughter now has the car at school (about 3.5 hours away) and it had about 130k miles on it at that time. This time it failed hard - once the light came on, the car stalled 10-15 minutes later when the battery went dead.

Unfortunately, since I was not there to work on it, we had to have it towed to a repair shop that I knew. They tested everything and agreed that the alternator was bad so they replace it. Everything was good.

Now fast forward to today. Actually, last week, her battery died - no light, just would not start. That was expected though since the battery was nearly 3.5 years old. We replaced the battery and all was good again.

My daughter drove home for the weekend and was on her way back to school this evening when the battery light came on again. Fortunately, she was only about 25 miles from the house so I told her to turn around and come back home. She got back home with no problem but the light was on the whole time.

When she got here I checked the battery voltage with the motor running, the headlights on, and the A/C and radio on. It measured 10.8V - clearly not charging at all. I shut the car off for about 15 minutes and then measured 11.8V. Started the car again and the light came on immediately - battery voltage measured around 11V.

Looks like I will be changing the alternator again...

Its funny, the factory alternator lasted a little over 4 years and 70K miles; my first replacement (that I did myself) lasted 3.5 years and nearly 60K miles; and the last one (from the repair shop) lasted 1 year and about 10K miles. I'm not sure if there is a moral to this story or not.

So I guess I will be calling around for alternators in the morning...
 
#24 ·
That's odd. My wife's car has 130k on the original alternator, mine has 115k on the original.

May want to bite the bullet and buy a factory alternator. With the experience you've had, not sure if continue to try aftermarket replacements.
 
#25 ·
I thought about that but the dealer cost is just astronomical and I don't have time to wait for one via mail.

Actually, as I mentioned in my earlier post, my original factory alternator only went 70k. The first (rebuilt) replacement went 60k and the supposed "new" aftermarket went 10k (but was installed by a repair shop, not me). That doesn't really instill enough confidence in a "factory" replacement to pay 4-5 times the price of an aftermarket one... In fact it does just the opposite. It definitely reinforces my belief that for simple stuff like this, I trust myself to do it far more than someone else.

So, no one around here had a new replacement in stock so I picked up another "re-manufactured" alternator and put it in yesterday am. It was about 1.5 hours including removal, calling around, going to get it, and installing the new one.

It, like the first replacement, comes with a Lifetime warranty. Hopefully, if it fails again, I will be available to do the work.

It's charging fine now - 13.9 to 14.3 at idle and no trouble light. All good for now.

It idles a bit rough when warm but it was doing that before. But that is another topic for another thread altogether...
 
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