That's normal. It's in your manual about the charging system and how it adapts its output based on demand.

And your gauge when the truck is running is no longer displaying voltage. It is simply a range from low to high. Note the larger areas on the center top of the gauge.

 

This should all be explained in your owner's manual...

Battery Load
Management
The vehicle has Electric Power Management (EPM) that estimates the battery's temperature and state of charge. It then adjusts the voltage for best performance and extended life of the battery. When the battery's state of charge is low, the voltage is raised slightly to quickly bring the charge back up. When the state of charge is high, the voltage is lowered slightly to prevent overcharging. If the vehicle has a voltmeter gauge or a voltage display on the Driver Information Center (DIC), you may see the voltage move up or down. This is normal. If there is a problem, an alert will be displayed. The battery can be discharged at idle if the electrical loads are very high. This is true for all vehicles. This is because the generator (alternator) may not be spinning fast enough at idle to produce all of the power needed for very high electrical loads. A high electrical load occurs when several of the following are on, such as: headlamps, high beams, fog lamps, rear window defogger, climate control fan at high speed, heated seats, engine cooling fans, trailer loads, and loads plugged into accessory power outlets. EPM works to prevent excessive discharge of the battery. It does this by balancing the generator's output and the vehicle's electrical needs. It can increase engine idle speed to generate more power whenever needed. It can temporarily reduce the power demands of some accessories. Normally, these actions occur in steps or levels, without being noticeable. In rare cases at the highest levels of corrective action, this action may be noticeable to the driver. If so, a DIC message might be displayed

 

Thanks Mark for the info you saved me $500 bucks

 

IOW's..............RTFM!!!!!!

 

Fyi, trucks and suvs have had this type system since 2005 model year.

 

Thank you RedSLEd for the explanation but we have driven this rig for 20,000 miles to California twice and Wyoming once. The volt meter always stays at the center of the meter. Now it moves and when it is to the left at about 1/4 of the full gauge reading it is charging the battery at 12 volts. I know that a proper charging rate is around 14.2 volts. Today my wife drove it about 22 miles to town today, no stops , no air conditioning and the volt meter jumped twice from 12 to 14 volts and it coincides with the volt reading on the pos and neg terminals on the battery. I ran jump wires from the terminals on the battery to my fluke meter in the cab to verify charging rate. It is suppose to get hot on Monday so I will take it out with the AC on high and see what happens. We just received a new 2020 Cat dozer and I swear the electronics are as complicated as my pickup. I am going to have the operator monitor the volt meter on Monday and see if it moves

 

It is in fact normal... It does it on my 2013...

If you want stable output, just open the headlights. It send a command to the computer to keep the alt at 14V.
I've done my research/test on this subject!

 

Read your owners manual. It's 100% normal. Just because you never noticed it doing it before doesn't mean it's wrong.

No need to look further into it.

Gm has installed this system in trucks for almost 20 years now.

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from GM service advisory years ago.......

Models: 2005-2009 Cadillac Escalade Models

2005-2009 Chevrolet Avalanche, Silverado, Silverado Classic, Suburban, Tahoe

2005-2009 GMC Sierra, Sierra Classic, Yukon Models

Voltmeter Fluctuation Condition:
Some customers may comment that the voltmeter is fluctuating between 12 and 14 volts on their full size pickup or utility vehicle. Starting with the 2005 model year, light duty full size pickups and utilities are equipped with a new Regulated Voltage Control (RVC) system. This system reduces the targeted output of the generator to 12.6-13.1 volts when in "Fuel Economy Mode" to improve fuel economy. The generator may exit "Fuel Economy Mode" if additional voltage is required. This will cause the voltmeter to fluctuate between 12 and 14 volts as opposed to non-regulated systems that usually maintain a more consistent reading of 14 volts. This fluctuation with the RVC system is normal system operation and NO repairs should be attempted.

Camper/Trailer Battery Charging Concerns:
Some customers may comment that when towing or hauling a camper/trailer, the auxiliary battery for the camper/trailer will not stay charged. In most cases, this concern is blamed on the new RVC system. While the RVC system does reduce the generator's targeted output voltage to 12.6-13.1 volts when in "Fuel Economy Mode", this feature is bypassed if the tow/haul feature is enabled. With the tow/haul feature enabled, the RVC system will stay in "Charge Mode" and the targeted generator output voltage will be 13.9-15.5 volts, depending on the battery state of charge and the estimated battery temperature. To keep the generator in the "Charge Mode", use either of the following two methods.

• The first method is to use the tow/haul mode when towing or hauling a camper or trailer.

• The second method is to turn on the headlights, which will increase the generator's targeted output voltage to 13.9-14.5 volts.

 

As stated above, perfectly normal. The owners manual tells you all about the truck.

 

Thank you GBLsierraSLE for the explanation but we have driven this rig for 20,000 miles to California twice and Wyoming once. The volt meter always stays at the center of the meter. Now it moves and when it is to the left at about 1/4 of the full gauge reading it is charging the battery at 12 volts. I know that a proper charging rate is around 14.2 volts. Today my wife drove it about 22 miles to town today, no stops , no air conditioning and the volt meter jumped twice from 12 to 14 volts and it coincides with the volt reading on the pos and neg terminals on the battery. I ran jump wires from the terminals on the battery to my fluke meter in the cab to verify charging rate. It is suppose to get hot on Monday so I will take it out with the AC on high and see what happens. We just received a new 2020 Cat dozer and I swear the electronics are as complicated as my pickup. I am going to have the operator monitor the volt meter on Monday and see if it moves

A Cat dozer has nothing to do with your truck.

Are we to assume you are either not listening to all these comments or you actually want something to be wrong with your truck? From what you have described, the truck is operating 100% normally, as it was designed to operate. It's charging at 12 volts because the battery is fully charged and/or getting hot and the extra voltage is not required. It only charges at 14+ volts when needed. It lowers the charge output to help prolong your battery life. Think of it as a battery tender charging system... it charges as needed and only when needed... as explained herein and in your owner's manual.

 

My voltage drops down to around 4 volts when the fan comes on and starts to get hot.
And this is normal??

 

For peace of mind you can load test the battery 2-3 times consecutively. If it passes the battery is probably ok. The alternator should output 14+ volt after until the battery is completely charged and averages low load, then drop.

 

My second comment was #5 comment now there have been 12 I will accept all the explanations as being correct. I can understand when you mention it is a fuel economy thing and I pull a trailer much of the time in the trailer mode so the economy mode is not in effect then. Well this is good, I was dreading having to go to the GM dealer, have not had a problem with pickup yet. I looked up this in my Cat manual, I believe it has a similar EPM system because it too was referring to battery temperature in hot weather conditions. We are going to monitor the volt meter tomorrow, going to be 95 degrees tomorrow in the pit.

 

Why do you keep bringing up your tractor?

Why did it take several replies on a forum to convince you it was working.

READ your owners manual that's in your glove box. You wouldn't believe how much info gm put in there just for you.

And when you put the truck in tow/haul mode. It turns off the system... again, explained in your manual.

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Maybe he doesn't know where the glove box is!!!

 

Its a copy CAT!

 

Or maybe there's just gloves in the glove box....no owners manual...

 

God bless the internet.

https://my.chevrolet.com/content/dam/gm ... manual.pdf

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Hello All,
I just had the same experiences as above, for 3.5 years the volt meter never moved until battery went dead and was replaced by Chevy Dealership last Monday 10/3/22 . However the battery is only 6 days old and has started the symptoms described above, and on my 300 mile trip home from Vegas the volts were down to less than 12 and the truck would not shift properly, but no warning lights have ever come on. Also this morning the volts were at 15+ when I started the truck. Would this be indicative of a going bad alternator or onboard voltage regulator?

 

If your truck is newer than 2005, the system seems to be working as designed. Alternator output is controlled by the BCM. Charge rate will vary from 12 to 15+ volts as needed, based on various factors, as is explained at least 2-3 times in this thread and in your owner's manual.

Not shifting properly? What does that mean? What year truck? How many miles on it? Has the trans ever been serviced?

 

Hi There, 2018 1500 4x4 with 67k miles. Company provided Enterprise Fleet vehicle When the voltage gets down to the lower end of the volt meter shifts take a long time to happen. typically sits at around 4000 rpms for about 10 seconds or until you hit the accelerator. also would not downshift correctly if the cruise control was active. Engine runs noticeably rougher when the volt meter was on the low side as well. This truck has been "rock solid with none of the above " for the last 3.5 years and all of a sudden this stuff is now happening. This is my first Chevy truck, since 1988. Thank you for your help.


Hi There,
2018 1500 4x4 with 67k miles, this company provided truck has been mine for the last 3.5 years and has been "Rock Solid with none of the above issues until last week". I drove the truck from Florida to Phoenix, on my way off of I40 at Winslow, AZ I noticed for the first time ever that the Volt meter was moving towards less than 12v. This is when the shifting started to act up, not downshifting when going down steep grade on cruise. Also shifting took long times in between gears and would stick in gear and not upshift at 5k RPM's unless I tapped the accelerator. So took it to the dealer, came back as a bad battery & AC compressor leak. Got the truck home, then off to Vegas. All good for about 2 hours then the Volt meter started to move downwards, but everything was still working, so I finished the trip to Vegas. Then time to come back, started the truck and the Volts were at 15+ for about 10 minutes back to center this lasted about 3 hours then about 60 miles from home the Voltmeter was heading south again to just above the lower limit, about 15 miles from the dealership the Shifting started to act up just like before and acceleration was very slow. With a noticeable difference in idle quality at stop lights, but I will credit the truck it got me too the dealership.
This is my first Newer Chevy & newer vehicle since my 2005 Dodge ram which I just sold.

thanks for listening to the above, I have to go back to Florida on Monday and do not want to break down on the way.

 

fluctuating voltage meter !! Electrical .. why can’t they just at fix the issue

 

Because there is no issue to fix. The system is working as it's supposed to, as has been explained several times in this thread.

 

just experienced this issue today coming home from Missouri...100 degree day pulling a small teardrop style camper.... after reading this... i now feel much better 2020 trailboss 5.3 litre... 27500 miles

 

The computer manages the charging system.
The system is not a simple voltage regulator like in the 'good old days'.

The computer WILL give a message if there is an issue with the charging system.

The upfitter docs have several pages of information about how the charging system works and what it can/does change.

 

thanks a bunch....

 

I have this issue on a 2005 silverado 6.0L.
Never had the fluctuations before. Been getting battery not charging pop up on occasion.Head Lights and dash lights fluctuate also at night. Alternator is a few years old and the battery is 6 months old. And the charge needle jumping back and forth all recent events.