Weird Voltage Fluctuations

[Blackout67]

Have an 05 Sierra 1500 Base model and of course it has horrible side Post battery with a short little bolt so you can't connect any accessories.
So I bought a Deka Intimidator Group 78 dual post so I could connect my amp. On the way to work yesterday the voltage was steady. Didn't go below 14 volts. But about half way to work it was going up to 15 volts but in the way home it was fine.
Today I started the truck up and it was fine but then it eventually started going down. Styrd between 12.8 and 13 volts. No music on, headlights off.
Came up to some traffic and was going about 10 mph and it jumped up to 14.4 for a few minutes then back down to 13.
Is this alternator problem or is the battery defective? Checked all connections when I got to work, no shorts, no blackening that would indicate the battery posted shorted .

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[winkychevelle 10+ year member]

They all do that. That is normal thank the epa for milage mandates. Gm shut the the alt off to get that .01mpg more efficiency

 

[Blackout67]

They all do that. That is normal thank the epa for milage mandates. Gm shut the the alt off to get that .01mpg more efficiency

I did not know that. How does it decide when to turn back on? I'd like to listen to music and I don't want to be feeding my amp 12.5 volts

 

[2RZ-FE 10+ year member]

You can find brass extended side post bolts that replace the small one and it has a nut so you can tighten down ring terminals

 

[winkychevelle 10+ year member]

I did not know that. How does it decide when to turn back on? I'd like to listen to music and I don't want to be feeding my amp 12.5 volts

Depends on the year but the pcm bypass for my 2013 was simple enough.

 

[Blackout67]

Depends on the year but the pcm bypass for my 2013 was simple enough.View attachment 46034View attachment 46035View attachment 46036View attachment 46037

I did some research on the pcms and apparently starting at my year there is voltage regulator that kicks on in "fuel economy mode" which i didn't know was a thing in the earlier years. According to a tab on the Silverado forums and putting on the headlights takes it out of the fuel economy mode. I will test this when I get off work on my way home