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Other than the Tahoe Limited Edition, the vehicle was redesigned for the 2000 model year on the new GMT800 platform, still shared with the full-sized pickups and SUV's.

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"Battery not charging" light when the battery + alternator are fine

My 2004 GMC Yukon shows “Battery not charging” rather frequently on the dash but by all measures, the battery and alternator are fine.

  • I’ve got a steady 14.6v every place I can measure when the car is running
  • 12.6v when it’s not
  • I’ve checked AC ripple with the car on and see none.
  • The battery voltage gauge on the dash shows the same things I measure (12.5v when off, 14.5 when running)
  • The light is obviously wrong, but its weird that the system which is telling me its not charging (via the light and message) is also telling me that it’s fine (via the gauge).

Anyone know how it could be thinking the battery isn’t charging even though it is?

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Hi @danielbeardsley ,

Don't know the vehicle or the answer but was wondering if the output from the voltage regulator is also fed to the BCM which then operates the warning light in the instrument cluster.

If, for example, it were a loose connection into the module (in the BCM harness connector perhaps) then when it went open circuit the module would turn on the warning light to indicate a problem with the charging voltage even if as you say there isn't one.

Here's a link to the repair manual for a 2007 Yukon (not your model year I know but perhaps it is similar in concept). The electrical sections weren't of much help in this instance except to say that a control module is used as an interface to the instrument cluster.

It did mention that you need to use the power distribution schematic and the power moding schematic (apparently power moding is used by the BCM to ensure values are correct against set parameters) to locate wiring problems, but I cannot find them, you may have better luck..

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Daniel Beardsley will be eternally grateful.
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