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Discussion Starter #1 (Edited)
So I noticed my voltage gauge moving around a bit yesterday, and seeing as I'm new to the diesel world, thought I'd ask here if this is a problem or not.



I guess you have to click the picture above and it will take you to my photobucket page, where the video will play, Can't figure out how to embed it.

As you can see in the video, the gauge is moving around a bit. This is from a cold start with the outside temp at around 63 degrees. I don't drive my truck as a daily driver, and it had sat for about 2 weeks since being started last. I was just sitting there at an idle letting the rig warm up a bit before taking off, radio was on as was the A/C when I noticed this.

I didn't notice any other "side effects" or issues and once I had driven around for a few miles and came back to an idle, the gauge was right above 14 and stayed there.

Thoughts?
 

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It will be low (around 12v) at startup and will raise to around 14v after about 30 seconds or so due to glow plugs & intake heater.
 

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Discussion Starter #3
It will be low (around 12v) at startup and will raise to around 14v after about 30 seconds or so due to glow plugs & intake heater.
Ah good to know. It just seemed odd that it was moving so much, but yeah between glow plugs and the heater your right it would be drawing a bit off the batteries/alternator.

Thanks for the info, just wanted to make sure I was ignoring something that could be potentially bad.
 

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I'm That Guy...
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As long as you stay above 12v I wouldn't worry, if it starts dropping below 12v I would look at replacing the alternator.

You might just check the grounds and power connections to make sure everything is tight as well. Check at the battery, starter, alternator, and the grounds.

Voltage is regulated and you will see fluxuation. Typically a working alternator will run around 13.9v and battery will be around 12v.
 

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X^^^^ he's dead on:thumb
 

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could the gauge fluttering like that be a sign of a bad battery?
I doubt it, because it's running off the alternator. You will see some fluxuation as you drive as the voltage regulator takes time to adjust the voltage output. Usually I think the fluxuation is only a few tenths of a voltage though, but I haven't watched it in awhile.
 

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reason im asking is my gauge will run above 14 and flutter sometimes but it lasts longer than just a few seconds, i got a p0802 code (could be battery related?) and my pass side battery looks like its leaking a tad. so im wondering if the battery could cause the higher voltage, flutter, and the p0802
 

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reason im asking is my gauge will run above 14 and flutter sometimes but it lasts longer than just a few seconds, i got a p0802 code (could be battery related?) and my pass side battery looks like its leaking a tad. so im wondering if the battery could cause the higher voltage, flutter, and the p0802
You can pull the battery and test it, but it shouldn't create a higher voltage. If you put a multi-meter across the battery you will probably read between 11.5-12.5 volts.

Leaking is possibly batteries boiling over which could be from overcharging from alternator if you are consistently over 14 volts.

I would check all connections and then take the truck somewhere to test batteries and alternator for issues. Maybe the alternator is over excited?
 

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I'm a GM Service Adviser and if I had a dollar for every time people freaked out about this gauge fluctuating I would be a wealthy man. It is completely normal. From 2005 up the trucks/suv's have a "Regulated Voltage Control System". It reduces alternator output to 12.6-13.1 volts when in "Fuel Economy Mode". Fluctuation from 12-15 volts is completely normal.
If additional voltage is required the voltage will bump up.
To override this if desired you can either engage tow/haul or turn the headlights on.
 

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long as it doesnt go over 14.2-14.2 volts your fine. You will have voltage drop from the alternator to the battery terminals everytime.

If youd like to check your batteries you can test them, then use a DMM to do a voltage drop test from the post to the terminal on each battery, add up all your values and you should have less than .10 between them.

id say you have nothing to worry about though
 
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