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Charging system not working under load while the A/C is on

Tiny
JEREMYH141520
  • MEMBER
  • 2009 CHEVROLET SUBURBAN
  • 5.3L
  • V8
  • 2WD
  • AUTOMATIC
  • 230,000 MILES
If I turn off the A/C it will charge fine. If I am cruising under 1,500 RPM's it charges fine with the A/C on. The engine ends up shutting off when you come to a stop. I am assuming because of lack of power. But the battery is fine. It never has a problem starting. Any help would be appreciated.

Thank you.

Jeremy
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Tuesday, September 1st, 2020 AT 6:13 AM

9 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning,

What is the voltage at the battery with the engine running and the A/C off?

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Then check it with the A/C on and tell me the reading.

It may be the alternator.

https://www.2carpros.com/articles/how-to-replace-an-alternator

The stalling may be a different issue.

https://www.2carpros.com/articles/stall-at-idle

Roy
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Monday, April 19th, 2021 AT 10:44 AM
Tiny
JEREMYH141520
  • MEMBER
  • 5 POSTS
The alternator is new. I changed it a few days ago.
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Monday, April 19th, 2021 AT 10:44 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Okay, good. I still need the voltage numbers I requested.

Roy
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Monday, April 19th, 2021 AT 10:44 AM
Tiny
JEREMYH141520
  • MEMBER
  • 5 POSTS
14.65 with the A/C off and 14.55 with it on. But now the dash says to service battery charging system. That just started when I turned on the vehicle to check the voltage.
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Monday, April 19th, 2021 AT 10:44 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Okay, 14.55 is good. All that means is that the alternator is adding more amps to the battery from the load and when that happens the voltage drops a little.

Do you have a scan tool or code reader? See if there is any codes set.

Roy
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Monday, April 19th, 2021 AT 10:44 AM
Tiny
JEREMYH141520
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P0121 is the only stored code.
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Monday, April 19th, 2021 AT 10:44 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Okay, the BCM and ECM work together with the charging system.

I believe the old alternator was your issue. I attached the info on the system.

According to this information, the light should go out on its own.

Roy

SERVICE BATTERY CHARGING SYSTEM

The BCM and the ECM will send a GMLAN message to the DIC for the "service battery charging system" message to be displayed. It is commanded ON when a charging system DTC is a current DTC. The message is turned "off" when the conditions for clearing the DTC have been met.
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Monday, April 19th, 2021 AT 10:44 AM
Tiny
JEREMYH141520
  • MEMBER
  • 5 POSTS
Thank you for your time and help.
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Monday, April 19th, 2021 AT 10:44 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
You are welcome.

Always glad to help.

Roy
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Monday, April 19th, 2021 AT 10:44 AM

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