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Old 25th August 2009, 21:30   #1
Mike S.
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Battery symbol flashing / Failing alternator?

I bumped a really old thread yesterday on this topic, but thought I would start my own since, well, I felt like it. :-)

To see my comments there, visit:

Battery Symbol Flashing ??

Anyway, yesterday my battery symbol was flashing while waiting in line to pick up the kids from school. It was hot. Darn hot. I consulted my owner's manual and it did not specifically mention a flashing battery symbol, just the battery symbol in general. So I came home, did a search, and found the thread above.

This afternoon, I decided to to some checking around.

Step One: Check battery voltage -- The car had been sitting in the garage since yesterday, and the voltage as measured at the battery was 12.33 V DC.

Step Two: Check for loose battery cables -- Lo' and behold, the negative battery cable was loose. So I tightened it up good.

Step Three: Start car, select test number 9 from the secret menu and have a look.

At idle, upon startup - 13.2 V to 13.3 V
At 3K - 3.5 K RPM - 13.5 V to 13.7 V as I cruised around the neighborhood
At idle, upon returning to garage - 13.5 V

Now, based on what I'm seeing, I am thinking that my alternator is charging. But as I said in the previous post, electrics are like a foreign language to me. Does what I am seeing make sense?

I would like to think that the ultimate culprit was the loose negative battery cable. Logic tells me that the alternator would not be able to charge effectively with a loose cable in the system, so maybe that's what caused the lamp to flash.

I'd love to hear other folks' opinions.
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Old 25th August 2009, 22:27   #2
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From what you have said, I would check the voltage at the battery using your volt meter, while the car is running and at different rpms. If it is still around 13.5, thats not super strong, but you shouldnt be getting a light. Check the belt tension. Maybe a tensioner is going bad and the belt is slipping. If you still dont find anything amiss, try loading up the electrical system with lights, A/C blower on high, radio, etc. and check the voltage at the battery again. If its low 13's then I would suspect a regulator or alternator. If you have high miles I would replace them at the same time (a new alternator comes with the reg).
Or, maybe you were lucky and the loose cable was the problem.



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Old 25th August 2009, 23:30   #3
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Quote:
Originally Posted by Flybot View Post
From what you have said, I would check the voltage at the battery using your volt meter, while the car is running and at different rpms. If it is still around 13.5, thats not super strong, but you shouldnt be getting a light.
Good idea. I'm not entirely sure what test #9 is showing me. I don't know if it's showing alternator output or just the overall state of the system, or even it's best guess at the battery voltage.

Quote:
Originally Posted by Flybot View Post
Check the belt tension. Maybe a tensioner is going bad and the belt is slipping. If you still dont find anything amiss, try loading up the electrical system with lights, A/C blower on high, radio, etc. and check the voltage at the battery again. If its low 13's then I would suspect a regulator or alternator. If you have high miles I would replace them at the same time (a new alternator comes with the reg).
I will be checking the belt and tensioner. When I was driving around the neighborhood, the A/C was on but no lights/radio/etc.

Quote:
Originally Posted by Flybot View Post
Or, maybe you were lucky and the loose cable was the problem.
Well, I hope so. I'm not looking forward to springing for a new alternator. I priced one from Tischer last night at about $650. I've heard rebuilds aren't a good choice, nor are aftermarket alternators.

What I gather, also, from your post is that I should be seeing higher than 13.5-.7 V on test #9?
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Old 25th August 2009, 23:56   #4
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Not sure if this will help, but thought I'd share my blinking battery light story. I bought my 2000 M5 four years ago as a CPO, and almost immediately the battery light started flashing. The stealership told me there was nothing wrong with it, but as soon as it was out of the CPO warranty, and going back in for new Cats under warranty, they tried selling me a new alternator. Decided against it, and to this day the battery light goes between off, flashing and constantly on. Since I've had it, two dealerships, Edge Motorworks (my regular) and Dinan have all told me they cannot find anything wrong with it. I guess one of these days the alternator will go, and I'll be sitting on the side of the road somewhere
, having ignored all the signs!!
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Old 26th August 2009, 00:06   #5
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Thanks for the reply. Did you, or do you, notice that when the battery light flashes that your idle speed begins to vary up and down? Not a great deal, but 100-200 RPM? And does heat cause the problem to manifest itself more?
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Old 26th August 2009, 00:18   #6
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Sounds to me like the brushes are about done inside the alternator if its doing it more with heat. I have always used a good quality rebuilt alternator and never had a problem. I would get a Bosch if thats what you have now. Just order it from a "real" parts store. You know, where an indy would get it. Not Pep Boys. They are cheapest because they are Chinese rebuilds and you dont know what your getting.
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Old 26th August 2009, 00:34   #7
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Quote:
Originally Posted by Mike S. View Post
Thanks for the reply. Did you, or do you, notice that when the battery light flashes that your idle speed begins to vary up and down? Not a great deal, but 100-200 RPM? And does heat cause the problem to manifest itself more?
I'll try and track it and see if I can figure any commonalities out. I do live in the East Bay of San Francisco area, where it's hot during the summer (high 90's most of the time). But I believe it does it during the winter also.

I'm thinking of getting the vorstiener hood, which would help reduce the temp in the engine bay, so will be interesting to see if that puts an end to it.

Will post updates as I figure them out.
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Old 26th August 2009, 00:41   #8
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Quote:
Originally Posted by Flybot View Post
Sounds to me like the brushes are about done inside the alternator if its doing it more with heat. I have always used a good quality rebuilt alternator and never had a problem. I would get a Bosch if thats what you have now. Just order it from a "real" parts store. You know, where an indy would get it. Not Pep Boys. They are cheapest because they are Chinese rebuilds and you dont know what your getting.
I guess that's certainly possible. I've had alternators go out before, and so I have sort of an idea of how they work.

But what I am having difficulty finding is what the voltages should be. Call me curious, or a PITA, but I would like to be able to learn something while I futz around with this. I've tried TIS and can't find anything in there. Of course, I'm sure that means I'm not doing something right. That thing has tried my patience more than once.

Rockauto.com has a reman Bosch unit for $348 minus the core. So that could be a route to go, if I needed to.
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Old 26th August 2009, 00:46   #9
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I dont know what the spec voltages are, but you have to have more than the battery voltage to charge it. I put a rebuilt alt on my 528 last week and it put out 14.6 volts. I would say thats on the high end. I think "normal" is 13.5-14.5.
Please post if you find the Book Answer.
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Old 26th August 2009, 01:07   #10
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Quote:
Originally Posted by Flybot View Post
I dont know what the spec voltages are, but you have to have more than the battery voltage to charge it. I put a rebuilt alt on my 528 last week and it put out 14.6 volts. I would say thats on the high end. I think "normal" is 13.5-14.5.
Please post if you find the Book Answer.
Right. That's what I figure, too.

So if the battery voltage is 12.33 V when the car is not running, and test #9 shows, on average, 13.5 V, I would think my system is charging.

Now, is it charging the optimum amount? That I don't know. Has it always been this way, and I just got the light because of the loose battery cable? That I also don't know.

I will see if I can check voltages at the battery at various RPMs just to be sure about what I'm seeing.

And yes, if I find the book answer, I will certainly post it.

I appreciate you help with this.
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