Voltage Fluctuations - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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  #1  
Old 06-10-2010, 11:23 PM
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Voltage Fluctuations

BORKED

it dips below the lowest point than this video shows, but this gives you an idea of what i'm dealing with.

what do ya'll think think is the matter? generally the voltage doesn't stray much farther than 14.4 volts, which i think is normal, but when it spikes it goes to 15.8. the low point goes down to below 12. i'll be putting a volt meter to the auto plug adapter and recording the readings soon just to verify that the gauge isn't malfunctioning.
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  #2  
Old 06-11-2010, 12:52 AM
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Put the meter right across the battery terminals for a better test of reality.
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Old 06-11-2010, 06:40 PM
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voltage stays in the 14.4 ballpark when driving.

when parked w/light on, 13.9 was lowest i saw.

battery only, before start, 11.2

battery only, after start, 12.2

....

Should i replace the battery first, then the alternator?
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Old 06-11-2010, 09:29 PM
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Quote:
Originally Posted by blckshdw View Post
I replaced my battery about 2 months ago, and I've had those odd fluctuations at idle since then, so I'd say alternator first.
what is your battery voltage like?
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Old 06-11-2010, 10:03 PM
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Quote:
Originally Posted by the roadie View Post
Put the meter right across the battery terminals for a better test of reality.


As long as it stays at about 14 volts while driving, don't sweat it.
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Old 06-11-2010, 10:48 PM
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Does the dash gauge voltage fluctuations mirror voltage measurements taken with digital VOM directly from battery posts?
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Old 06-12-2010, 09:56 PM
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disconnect battery and check voltage at battery leads if it still fluctuate then its the voltage regulatein the alternator
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Old 06-14-2010, 02:26 AM
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idle voltage with no lights went as low as 13.6 when i hit the lights, it dipped to 12.7 then came back up to 13.8 or so. while driving it's regularly 14.4. it's when i let off the gas SOMETIMES the voltage will drop WAAAAY down. it's hard enough getting voltage readings while driving so unfortunately i've not been able to reproduce that condition.

the battery in the morning is quite low at 11.something. voltage drops to sub 10.0 when starting. Advance says the alternator is working, pushing 3-4 amps to the battery, holding 13.9 volts...

frustrating. i'd rather not be waiting for something to fail when i'm 300 miles from my garage heading to a race... i like my truck like i like my bike. ready to go at a moments notice, dependable.
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Old 06-14-2010, 09:43 AM
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How old is your battery? The one in my 2004 was original (based on the date
code), and died over Christmas. I didn't experience the fluctuations
you showed, but then again, my gauge has the dreaded stepper motor
disease... I have a plug in meter in my accessory socket, and it will
show definite fluctuations in voltage, even with the new battery,
just not what your video showed.

If you read 11.2V on a meter hooked up to the battery with the truck off,
that sounds like the battery isn't holding a charge. If you get around 13.8
or so once the truck is running, the alternator is pushing about the right
voltage. Don't go by the dash gauge. It's not a direct read off the
alternator or battery, but rather a translation through the PCM.

Not that I have a ton of faith in Advanced Auto Parts testing, but based
on what they said, it actually sounds like your alternator is putting out
the right voltage and current.

Good Luck!

Chris
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Old 06-14-2010, 09:58 AM
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Quote:
Originally Posted by christo829 View Post
How old is your battery? The one in my 2004 was original (based on the date
code), and died over Christmas. I didn't experience the fluctuations
you showed, but then again, my gauge has the dreaded stepper motor
disease... I have a plug in meter in my accessory socket, and it will
show definite fluctuations in voltage, even with the new battery,
just not what your video showed.

If you read 11.2V on a meter hooked up to the battery with the truck off,
that sounds like the battery isn't holding a charge. If you get around 13.8
or so once the truck is running, the alternator is pushing about the right
voltage. Don't go by the dash gauge. It's not a direct read off the
alternator or battery, but rather a translation through the PCM.

Not that I have a ton of faith in Advanced Auto Parts testing, but based
on what they said, it actually sounds like your alternator is putting out
the right voltage and current.

Good Luck!

Chris
new battery then. if the alternator is in the cards, a new battery would most certainly be in the cards anyway.

thanks for your help!
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