Charging voltage varies, alot....

[trammd]

I have a 2014 1500 LTZ Z71.

Brand new Battery installed AGM style 850CCA.

My charging voltage swings wildy. When I start up I get the alternator to battery charging voltage of 14.3 to 15.2 Volts. As the truck warms it will begin to fluctuate, I can watch the volt meter drop to 12.7 Volts (battery voltage) it isnt dependant on Loads, headlights. accessories etc. also not dependant on engine RPMs. It will drop to 12.7V then if I turn the truck off and restart it will start out at 14.7 V then after 3-4 minutes begin to drop...then after awhile it may return to 14+/

Really weird. The comman thread is by re-starting the truck it always starts at 14.4+ then after waiting it begins to drop.

any ideas?

The truck has 60K miles and the original alternator I believe.

[scott.moody.9401]

It's supposed to do that. Charging voltage will vary depending on battery charge state, temperature, etc. It's not static

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[trammd]

Thanks, my older vehicles never did that.

[g2full]

I noticed this with my 15 as well. Made me question if there was an issue starting to happen. Mine is more constant for each trip - but sometimes it'll be on the lower side, and other times where I would consider normal. Not use to something this new that operates like that. 

[garagerog]

This is not a new thing, variable charging rates controlled by the ECM have been in Silverados since 2005 if I'm not mistaken.

[ftwhite]

From my 2018 Owners Manual:

Voltmeter Gauge: When the ignition is on, this gauge indicates the battery voltage. When the engine is running, this gauge shows the condition of the charging system. The gauge can transition from a higher to lower or a lower to higher reading. This is normal. If the vehicle is operating outside the normal operating range, the charging system light comes on. See Charging System Light 0 147 for more information. The voltmeter gauge may also read lower when in fuel economy mode. This is normal. Readings outside the normal operating range can also occur when a large number of electrical accessories are operating in the vehicle and the engine is left idling for an extended period. This condition is normal since the charging system is not able to provide full power at engine idle. As engine speeds are increased, this condition should correct itself as higher engine speeds allow the charging system to create maximum power. The vehicle can only be driven for a short time with the readings outside the normal operating range. If the vehicle must be driven, turn off all accessories, such as the radio and air conditioner. Readings outside the normal operating range indicate a possible problem in the electrical system. Have the vehicle serviced as soon as possible.

[Z45]

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.

[Dr Awesome]

The old system apparently used to actually drain the battery while you were driving just to save on gas, then charge back up.  That was no good for batteries, they like to stay charged.  They have since changed it to vary based on the loads the truck is seeing, so you might need more power if you are using a trailer or powering things from your ports/outlet.  Either way, it is normal and you should be able to test it.

[trammd]

I don't think the battery is becoming discharged as the lowest voltage I have seen is 12.6.

 

[CadillacLuke24]

I've noticed this as well, not specifically to the output the OP has, but it will vary depending on outside temperature, engine speed, etc. My Battery tests well, and he fires up every time, so on I go!

[Senor Moore]

My 2017 silverado does the same. The only thing different is yesterday  i got a " check charging system." message after auto starting the truck and I got in, put the key in and turned it to the starting position.  I ran an errand turned the car off inspected battery and alternator conmections.  I started the truck and other than the exact fluctuation in the meter like the pic you posted I havent received any message today.  Im going to obey my truck and have it checked today though lol and I'll post back. I like the plugin volt meter you have.  

[pokismoki]

the high voltage is design as part of the charge/balance algorithm,  by charging at 15 volts this causes the individual cells in the battery to automatically balance themselves. so no cell is under voltage. it only last for about 30 minutes or about that. totally normal

[Joe-Bob]

I too experienced this issue with my 2017 Silverado LT 4x4 after replacing my dead battery. I had thought that maybe the battery was incorrectly installed but after careful checking it was not. The voltage fluctuations being read on the meter on the dash would fall short of 12 volts. I took the alternator into O'Reily's Auto Parts and had it tested. 3 out of 8 tests showed a fault with the voltage regulator so I replaced the alternator for some sense of security and not being left stranded with a possible dead battery. I also replaced the belt and tensioner since it is now a 5 year old truck. With a whole new set up, I'm still seeing the volt meter dip to 12 volts. Should I have replaced that expensive alternator after all?

[Frank winn]

I’m having the same issues however mine started when I left my one scan tool connected overnight and found a discharged battery the next morning. Used a jump box to get moving and have had charging issues ever since. Bought new alternator and battery. Inadvertently I left battery connected when I replaced alternator and shorted the hot side of the alternator while disconnecting, then replaced battery, had to replace fuse block on top of battery, continued to have under charging issues. Had to always have home battery charger connected while at home . One day I discharged battery (third or fourth time while driving) completely replaced battery and now system is over charging. I believe there is a second voltage regulator in ecm.  Because the alternator has been bench tested several times at o’reillys and charges within parameters.