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Charging issues

Leone1662

By Leone1662
in Troubleshooting & Recalls

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Leone1662 Enthusiast

Leone1662

Posted
Posted (edited)

2018 Silverado 2500 LT 1,300 miles

 

truck during the day shows volts at 12.5. I can turn on ac full blast, radio and defroster and colts stay at 12.5 all day. When driving volts stay at 12.5 when I’m rolling and foot of gas mpg gauge goes up to 99mpg then will charge at 14volts as soon as I hit the gas bolts drop to 12.5. And night when headlights turn on truck will charge at 14 volts. First two times truck was taken to dealer they said nothing is wrong now the third time they tell me that’s not normal and change alternator and never fixed the problem still in the shop. Anyone have same issues or volts stay around 13.2-14.5 volts all day and night

Edited by Leone1662
silveradosid Senior Enthusiast

silveradosid

Posted
Posted

the charging cycle is temperature related . a cold battery does not charge very well, below 45 degrees mine stays at 14 when it gets to 60 it will stay just under 14 and when it get to 70 and above it will always be just above the 12 volt range. i think gm does this because the hotter the temperature the faster the chemical reaction is in the battery which makes them sulfate and boil of the chemical in the battery which shortens the life of the battery

Leone1662 Enthusiast

Leone1662

Posted
  • Author
Posted

Idk about that where I live it hasn’t been above 60 and even if it’s 50 degrees out truck sits at 12.5 volts

sk Senior Enthusiast

sk

Posted
Posted

The system is actually designed to work like that and has been since around 2005.  Search back through these forums or just Google something like "GM charging system".  You can find very in-depth explanations of how the system works.  But under normal operation you can see anywhere between 12-14.4 Volts on the gauge.

sdeeter19555 Senior Enthusiast

sdeeter19555

Posted
Posted
The system is actually designed to work like that and has been since around 2005.  Search back through these forums or just Google something like "GM charging system".  You can find very in-depth explanations of how the system works.  But under normal operation you can see anywhere between 12-14.4 Volts on the gauge.
I've seen as low as 13.8vdc and as high as 15.2vdc, but never below 13.8vdc (which is the voltage of a "12 volt" lead acid battery).

That's looking at it through a stand alone monitor that is reporting the voltage the ECM/BCM is reporting. That's not a VOM...

2012 2500hd 6.0l CCSB 4wd
ChristopherDB Enthusiast

ChristopherDB

Posted
Posted

I was going to ask this same question today. I have a 2018 with 1500 miles and noticed the voltage guage is anywhere between 12.5 and 14v and it is constantly fluctuating. I've never seen/noticed this before in any of my other vehicles.

sdeeter19555 Senior Enthusiast

sdeeter19555

Posted
Posted

This was common in the Dodge Cummins-powered trucks when they started because of the cycling of the grid heaters...Dodge answered this customer complaint by make the in-dash voltage gauge read 14vdc all the time. That's right, they made the gauge useless...

Same with the oil pressure...it was a dummy gauge that read yes/no from a pressure switch (not a pressure sensor) and made up the reading based on engine rpm and temperature...what's worse is that the oil pressure gauge would read normal oil pressure for three minutes (when in reality the engine had zero oil pressure) before it would show a problem.

Essentially the Dodge dash gauges were glorified idiot lights...

Point being, I could see GM doing the same thing with too many customer complaints!

2012 2500hd 6.0l CCSB 4wd



ic3man5 Enthusiast

ic3man5

Posted
Posted

Charging System Operation
The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation and they include:
Battery Sulfation Mode

Charge Mode

Fuel Economy Mode

Headlamp Mode

Start Up Mode

Voltage Reduction Mode
The engine control module (ECM) controls the generator through the generator turn on signal. It monitors the generator performance though the generator field duty cycle signal circuit. The signal is a 5-volt pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-95 percent. Between 0-5 percent and 95-100 percent are for diagnostic purposes. The generator provides a feedback signal of the generator voltage output through the generator field duty cycle signal circuit to the ECM. This information is sent to the body control module (BCM). The signal is a 5-volt PWM signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-99 percent. Between 0-5 percent and 100 percent are for diagnostic purposes.

 

10% duty cycle = 11V

90% duty cycle = 15.5V

 

Startup Mode should be 14.3V for 30 seconds.

Headlamp mode will be 13.9-14.5V (I've seen this delayed coming out of lower voltages).

 

 

Lower voltage means your battery doesn't need to charge. If you are constantly sitting at 14.4V+ with hours of driving your battery is probably starting to go bad.

Leone1662 Enthusiast

Leone1662

Posted
  • Author
Posted

I had a 2016 with 38,678miles and charged all day everyday around 13.2-14.5 never had a battery issue. Now this one nothing different besides it’s an 2018Lt and the other was a 2016 Wt both had one battery and 220amp alternatorthe 18 during the day it’s at 12.5 and at night is 14.5. Can’t tell me battery is always charged during the day. Truck has 1,400 miles on it

  • 5 years later...
Josh B. Enthusiast

Josh B.

Posted
Posted

I have a 16 sierra denali. Been chasing a battery drain for several months. I've unwired everyrhing I have added to the truck. Replaced battery and alternator couple times. No results. I noticed it was only not charging properly during day time. My alternator will fluctuate from 11.5v to 14.5v. But most often less than 12v. Covered sensor and no more issues. Now what could be shorted or causing the issue? I think it would be easier to identify if it was happening during night mode. 

 

Thanks in advance

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