Charging issue

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Freakysyde11

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Joined
Aug 9, 2025
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Bakersfield, CA
Hi, I'm having big issue figuring this one out. 2006 GMC Sierra1500 I installed new alternator and Immeaditly it worked as it should charging between 13.6 and 14.1 for 1 day and now with new alternator im only charging at 11.8 tp 11.4 but about 20% of the time it will charge as it should. I have checked the usual, good battery, triple check battery connection and such. I am desperate here and hope someone can steer me in the right direction please
 
Check to see if you have a SARVC around the negative battery terminal. It's a kind of power monitor that tells the PCM when there is high current draw to increase the voltage. If you unplug it, it will let the alternator work like a regular one and keep the voltage at ~14V where it normally is.

Did you measure the voltage using a DMM or using the dash gauge? It's woefully inaccurate and I wouldn't count on it telling the truth. If when the voltage is lower and you put a bunch of loads on like HVAC blower, lights, brake lights, wipers and the voltage comes back up, I think your SARVC is working correctly. It's supposed to drop voltage when there are low power demands to save the battery.
 
Mooseman said:
Check to see if you have a SARVC around the negative battery terminal. It's a kind of power monitor that tells the PCM when there is high current draw to increase the voltage. If you unplug it, it will let the alternator work like a regular one and keep the voltage at ~14V where it normally is.

Did you measure the voltage using a DMM or using the dash gauge? It's woefully inaccurate and I wouldn't count on it telling the truth. If when the voltage is lower and you put a bunch of loads on like HVAC blower, lights, brake lights, wipers and the voltage comes back up, I think your SARVC is working correctly. It's supposed to drop voltage when there are low power demands to save the battery.
Click to expand...
I used my Multimeter to test. I am on my second alternator this week, and now this one is also showing bad. What could kill the alternator? I have checked all ground connections, even sanding and cleaning each one of them
 
Check your grounds. Go to charm.li and get the schematics for your main ground points under the hood.

What about the SARVC?
 
Mooseman said:
Check your grounds. Go to charm.li and get the schematics for your main ground points under the hood.

What about the SARVC?
Click to expand...
I have a question about the SARVC, so I just unplug it and it wont hurt anything else. I did find it and I am still having big issue with the truck. I had to have a tow truck get me and the truck home tonight spent 4 hours on the side of the road tonight because of the issue
 
Freakysyde11 said:
I have a question about the SARVC, so I just unplug it and it wont hurt anything else.
Click to expand...
You can safely unplug it. Your alternator, if it's good, will work like an ordinary alternator and not drop the voltage.

If voltage is still low, you have other issues. Found this other thread with similar issues:

Reprise

SOLVED! Thread 'Alternator not charging-not the alternator'

Put in a new HO alternator in the Sierra about a year ago, not long after I upgraded to dual e-fans.

Since then, I replaced the fan harness (the 'new' new one is fine), and up until today, my charging system was fine.

Today, I started the truck, had the (bus) issue where the radio doesn't output sound, and shut it off. It's very intermittent, and not (?) related to what I'm about to relay...

Restarted, and the radio worked again (as per normal), However, I immediately saw "battery not charging" on the info display, along with the battery lamp and the gauge pointing three notches from...

Readers Digest version:
Reprise said:
That little 11" cable (fusible link) between alternator stud and the red battery box was the culprit. Put the new one in, and voila! (that was for you, Moose... sorry, no diacritical :) Dash gage showed +14V charging, and the meter registered 14.23 at the battery terminals. Problem (should be) solved!
Click to expand...
 
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Mooseman said:
You can safely unplug it. Your alternator, if it's good, will work like an ordinary alternator and not drop the voltage.

If voltage is still low, you have other issues. Found this other thread with similar issues:

Reprise

SOLVED! Thread 'Alternator not charging-not the alternator'

Put in a new HO alternator in the Sierra about a year ago, not long after I upgraded to dual e-fans.

Since then, I replaced the fan harness (the 'new' new one is fine), and up until today, my charging system was fine.

Today, I started the truck, had the (bus) issue where the radio doesn't output sound, and shut it off. It's very intermittent, and not (?) related to what I'm about to relay...

Restarted, and the radio worked again (as per normal), However, I immediately saw "battery not charging" on the info display, along with the battery lamp and the gauge pointing three notches from...

Readers Digest version:
Click to expand...
did you put just the cable or the whole little red box
 
That wasn't me and that member is NLA. I would imagine he replaced just the fusible link.
 
Mooseman said:
You can safely unplug it. Your alternator, if it's good, will work like an ordinary alternator and not drop the voltage.

If voltage is still low, you have other issues. Found this other thread with similar issues:

Reprise

SOLVED! Thread 'Alternator not charging-not the alternator'

Put in a new HO alternator in the Sierra about a year ago, not long after I upgraded to dual e-fans.

Since then, I replaced the fan harness (the 'new' new one is fine), and up until today, my charging system was fine.

Today, I started the truck, had the (bus) issue where the radio doesn't output sound, and shut it off. It's very intermittent, and not (?) related to what I'm about to relay...

Restarted, and the radio worked again (as per normal), However, I immediately saw "battery not charging" on the info display, along with the battery lamp and the gauge pointing three notches from...

Readers Digest version:
Click to expand...
voltage is still low 11.6 and I can seem to figure this one out
 
Maybe your new alternator is a dud? It can happen. It did to me, similar to you. Worked a few days and then died. It was even an ACDelco rebuilt.

Just because it's new doesn't mean it's good. Take it out and have it tested.
 
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