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I have a 2015 GMC 2500 with around 90k miles. Last year some work was done on the truck by a local diesel shop (Cp3 Conversion, FASS, up pipes, downpipe, EGR plate, full 4"exhaust, tuning). Ever since then, every time I start the truck, I get a "low battery" message pop on the dash. The shop said that my batteries were fine, but they couldn't seem to figure out what was causing the code. I finally go tired of it and bought 2 new AGM batteries to see if it fixed the problem, and it did not. I also have dual alternators, which both seem to be working fine. Voltage stays right in the middle. Battery connections are all clean and secure. I checked ground connections and they all seem to be good too. Any other ideas? Or has anyone else ever experienced this?
 

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Check the Alternators with a meter. Just a piece of mind to rule them out. Ive seen it too many times where the dash says they are good but they dont test good. IMHO
 

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As I understand the problem, your dash gauge tells you that you have a proper charge on the battery, but you still get a message on the DIC saying "low battery" . Is that correct? Have you checked the battery voltage with a voltmeter? Both batteries are nearly the same, I presume?

I think this may be similar to the guy who drove his truck 50 miles to the garage because the message was 'no engine oil pressure - do not drive truck'. Upon arrival, it was noted that the engine sounded perfectly normal.

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my guess,the tune has something to do w/ it
 

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Is this what you're seeing?

Charge Indicator Operation
The instrument panel cluster illuminates the charge indicator and displays a warning message in the driver information center if equipped, when the one or more of the following occurs:
• The engine control module (ECM) detects that the generator output is less than 11bV or greater than 16bV. The instrument panel cluster receives a GMLAN message from the ECM requesting illumination.
• The instrument panel cluster determines that the system voltage is less than 11bV or greater than 16bV for more than 30bseconds. The instrument panel cluster receives a GMLAN message from the body control module
(BCM) indicating there is a system voltage range concern.
The instrument panel cluster performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds
 
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2017, 2500HD, LTZ, front guard, Duraflap mudguards, Leer bed topper
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Alternator (generator) puts out voltage and amperage...

maybe a discussion about the alternator output would be good to have..
 

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A bad diode in alternator or issue with wiring connection at alternator could cause this problem. To test alternator you need a oscilloscope to look for irregular sine wave. Since work was done to truck I would check continuity of wiring at alternator while moving plug looking for brittle wires or internal break.


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I have a 2015 GMC 2500 with around 90k miles. Last year some work was done on the truck by a local diesel shop (Cp3 Conversion, FASS, up pipes, downpipe, EGR plate, full 4"exhaust, tuning). Ever since then, every time I start the truck, I get a "low battery" message pop on the dash. The shop said that my batteries were fine, but they couldn't seem to figure out what was causing the code. I finally go tired of it and bought 2 new AGM batteries to see if it fixed the problem, and it did not. I also have dual alternators, which both seem to be working fine. Voltage stays right in the middle. Battery connections are all clean and secure. I checked ground connections and they all seem to be good too. Any other ideas? Or has anyone else ever experienced this?
Did you ever find the cause of this issue? I am having a similar issue. I also changed my batteries. It is driving me crazy as I have checked everything I can think of. I ruled out the alternator because I changed it about 30k miles ago. Hoping you have a solution.
 

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What is your charging voltage at idle after warmup? Monitor your voltage from startup until the engine is warm. Is your LTERM connector firmly attached at the alternator. New parts are not necessarily good parts. I hope you replaced your alternator with OEM.
 
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@RLeidel Did you ever find the cause? I have the exact same issue. Alternator is relatively new, batteries are new, voltage is good. At a loss and it's driving me nuts.
Probably won't get an answer from OP.
That's the only post OP ever made.
Hasn't been seen since that day (Apr 2021)
 

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Anyone actually have a code stored in the ECM? What is it?
 
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