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Battery light

Tiny
MOII
  • MEMBER
  • 2010 MAZDA 2
  • 1.5L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 110,000 MILES
Hi guys,


My battery light recently came on, I had the battery checked and it was fine. I was told that it may be the alternator so I had my mechanic check that but he said it's fine.

The volt is reading 13.50 with the engine running and 13.46 with the headlights on, engine running, Air condition and wipers.

The battery light goes off after driving for about ten minutes sometimes less

if both the alternator and battery are working as they should. What could be the cause of this?
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Tuesday, May 21st, 2019 AT 7:36 AM

12 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,878 POSTS
Welcome to 2CarPros.

Was the alternator checked when the light was on?

Joe
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Tuesday, May 21st, 2019 AT 7:58 PM
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

This could be a problem with your vehicle's Body Control Module (BCM). The BCM on your vehicle is what get the information from the sending unit and then either turns on your vehicle's battery warning lamp or doesn't. If this control module is failing or has an internal short, it could cause this problem. In the diagrams down below I have included a description of the BCM and how and what pins to test for the BCM. i have also included a link below for you if you are unfamiliar with how to use a multi-meter, as you will need one to do the diagnostic testing.

https://www.2carpros.com/articles/how-to-use-a-voltmeter

Please get back to us with what you are able to find out.

Thanks,
Alex
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Tuesday, May 21st, 2019 AT 8:14 PM
Tiny
MOII
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  • 7 POSTS
Hi, thank you for responding! I will advise my mechanic and get back to you.
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Wednesday, May 22nd, 2019 AT 7:04 AM
Tiny
MOII
  • MEMBER
  • 7 POSTS
JACOBANDNICKOLAS no, the light wasn't on when we checked the alternator.
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Wednesday, May 22nd, 2019 AT 7:07 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,878 POSTS
Welcome back:

If the light wasn't on, chances are the alternator is going bad and was working when checked. Honestly, if the light comes on, it is really easy to check the alternator. All you need is a volt meter or a multi-meter. Here are directions. Basically, at the battery, you check for voltage with the engine running and then turn the vehicle off and recheck it. When off, you should have right around 12v. With it running , you should see high 13V to 14v readings. If you don't confirm all wiring at the alternator is tight, not damaged, and not corroded and make sure the alternator belt is tight. If everything is good and you don't get the increase in voltage, most likely the alternator is going bad.

Here is the link.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Here are a couple links you may find helpful:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-check-wiring

Also, if you plan to replace the alternator, here is a link showing in general how it is done.

https://www.2carpros.com/articles/how-to-replace-an-alternator

Let me know if this helps or if you have other questions.

Joe
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Wednesday, May 22nd, 2019 AT 6:57 PM
Tiny
MOII
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  • 7 POSTS
JACOBANDNICKOLAS okay, thanks. I'll check it again when the light is on. I'll keep you posted.
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Thursday, May 23rd, 2019 AT 7:19 AM
Tiny
MOII
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  • 7 POSTS
If the alternator is going bad, do you think I should try to fix it or just get a new one?
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Thursday, May 23rd, 2019 AT 7:28 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,878 POSTS
Welcome back:

Honestly, just replace it. It isn't worth the repairs. If you have any luck like me, you will fix it and a week later, something different will go bad in it.

Please feel free to let me know if you have other questions or need help.

Take care,
Joe
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Thursday, May 23rd, 2019 AT 4:27 PM
Tiny
MOII
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Okay. One more question.I don't know much about cars, but I've heard of something in the alternator called the regulator. If that is the reason for the battery light to come on, do you still recommend getting a new alternator or just get a new regulator?
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Friday, May 24th, 2019 AT 7:01 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Welcome back:

The voltage regulator is an internal component of the alternator. It limits the amount of voltage produced by the alternator, which is more than you will need. With that, chances are the regulator isn't bad. Most times, the voltage regulator will cause the alternator to overcharge the battery. So yes, I would still replace the alternator.

Please feel free to ask any question you have. It's not a problem.

Take care,
Joe
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Friday, May 24th, 2019 AT 8:13 PM
Tiny
MOII
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  • 7 POSTS
I got the alternator replaced. Thanks for helping.
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Monday, May 27th, 2019 AT 7:08 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,878 POSTS
Welcome back:

I'm glad you got if fixed. Please let me know if you have questions in the future.

Take care,
Joe
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Monday, May 27th, 2019 AT 7:45 PM

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