Alternator problem running the voltage is low?

Tiny
TOM PARFREY
  • MEMBER
  • 2002 CHEVROLET TRAILBLAZER
I am having a problem with, my vehicle 4.2 6 cylinder. When running the voltage is low, it may swing as low as 12 volts at times and once in a while back up to 14 volts. Turning on high current accessories always makes it worse but it also happens intermittently without. I verified the volt gauge on the dash and it is okay. Using a dc clamp on amp meter on the alternator wire shows a large current output with accessories on but the voltage is low. Battery is six months old and was tested recently as good. Is it possible to have current output (40+ amps with accessories on) and have low voltage readings?
Wednesday, August 8th, 2007 AT 9:13 AM

9 Replies

Tiny
DENNYP
  • MECHANIC
  • 1,824 POSTS
This happens when the alternator is going out. Here is a guide and diagrams below to help you see what the job will be like on your car:

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

Check out the diagrams (below). Please let us know what happens.

Cheers
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Monday, November 5th, 2007 AT 9:20 PM
Tiny
SERGIO RUFFOLO
  • MEMBER
  • 1 POST
  • 2002 CHEVROLET TRAILBLAZER
My six cylinder LT model, is not holding a charge. I changed the alternator and battery and it still gives me a message that the battery is not charging and is alternator gauge is low. What is my next step? Thanks, Lou
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Sunday, July 22nd, 2018 AT 1:25 PM (Merged)
Tiny
FISHERMAN
  • MECHANIC
  • 937 POSTS
Re-check the alternator (bench test it).

Also be sure that you have a solid ground to the engine and the frame of your truck!

Nothing else besides that.

Good Luck
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Sunday, July 22nd, 2018 AT 1:25 PM (Merged)
Tiny
BPERRAS
  • MEMBER
  • 2 POSTS
  • 2002 CHEVROLET TRAILBLAZER
  • 6 CYL
  • AWD
  • AUTOMATIC
  • 85,000 MILES
When left over night it quite often drains the battery, I have replaced the battery four times in the last eight months and have had it to a GM dealership numerous times for days and days. But it never drains for them even when they keep it for a week. Yet when I get it home it drains within a day or less. Someone recently told me to replace the alternator and my husband tried to, but how the heck to you get it out of the spot it is in without taking half the vehicle apart to get it out? Do you need special tools as well? Has anyone else experienced this same problem?
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Sunday, July 22nd, 2018 AT 1:25 PM (Merged)
Tiny
DENNYP
  • MECHANIC
  • 1,824 POSTS
Do you leave the key in the ignition overnight?
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Sunday, July 22nd, 2018 AT 1:25 PM (Merged)
Tiny
BPERRAS
  • MEMBER
  • 2 POSTS
No I normally do not.
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Sunday, July 22nd, 2018 AT 1:25 PM (Merged)
Tiny
QUAD D
  • MEMBER
  • 1 POST
  • 2003 CHEVROLET TRAILBLAZER
Six cylinder four wheel drive automatic.

Any tips on how to remove the alternator?
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Sunday, July 22nd, 2018 AT 1:25 PM (Merged)
Tiny
MMPRINCE4000
  • MECHANIC
  • 8,548 POSTS
1. Disconnect negative battery cable.
2. Remove drivebelt.
3. Unbolt AC line mounting bracket at engine lift hook.
4. Remove the right engine lift hook and alt. Mounting bolts and alternator.
5. Disconnect electrical connectors from alternator.
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Sunday, July 22nd, 2018 AT 1:25 PM (Merged)
Tiny
NUCRBOMB68
  • MEMBER
  • 1 POST
Only thing that has to come out is the battery bracket, battery, and one bracket by the alternator.
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Tuesday, February 11th, 2025 AT 1:44 PM

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