Intermittent voltage level drop

Tiny
TOMENGELMANN
  • MEMBER
  • 2007 CHEVROLET TAHOE
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 170,000 MILES
The alternator light comes on and the voltage drops from 14 to 11 volts. The problem is intermittent. The battery has just been replaced. The alternator was replaced in 2017.
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Monday, June 22nd, 2020 AT 7:59 AM

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Tiny
KASEKENNY1
  • EXPERT
The way this works is the ECM contains the voltage regulator and it bases this on the input from the BCM. The BCM determines what voltage is needed based on the battery current sensor.

So this means if the battery current sensor is not reading properly, it will give the BCM faulty info and the ECM will not allow the generator to charge properly.

Also, it could be the BCM or ECM causing this issue.

The way to determine this is to test the alternator to determine it is capable of doing what it is asked to do. Even though it was replaced, that was 3 years ago and it could have failed.

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

Next is to hook up a scan tool and see what the BCM is seeing as the battery voltage this will determine if the current sensor is accurate or not.

Then we can tackle an ECM if all else checks out.
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Monday, June 22nd, 2020 AT 11:10 AM

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