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Intermittent Battery Warning Light

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I have experienced an intermittent battery warning light and every time I schedule a service appointment, it stops coming on. So I cancel my appointment and hope for the best. Before sit on the dealer’s doorstep and do a Chuck Norris, has anyone experienced this? Also, does anyone know if the warning light comes on with a system charging problem or also a weak battery AND a system charging problem? Thanks in advance.



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Most likely, problem could be:


  • An undercharged battery (many short trips, etc.)
  • A failing battery
  • A failing alternator
  • A slipping serpentine belt

Has the ECM firmware in your Legacy been updated per TSB 11-174-17R (battery discharge)?


The place to start would be to check the quiescent battery voltage with an accurate meter, then charge it overnight uusing a "smart" battery charger and check the battery voltage again (should be ~12.8 volts). Then check voltage at the battery with the engine running (should be ~14.3 volts).

Edited by ammcinnis

"If you don't know where you're going, any road will take you there." ~ The Cheshire Cat (Alice in Wonderland)


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Disclaimer, I have a 4th gen, but wanted to throw out my .02.


My legacy did this in the winter when it was cold out, it only does it with the weak oem battery that is about 1 year old. I suspect it happens when the voltage when cranking goes too low, because for my it'd go down to like 9.5 volts. Sometimes the light would only stay on for about 5 seconds after starting the car and go away, other times it would stay on, and not go away until I turned the car off and on.


Now that the weather is a little warmer, it doesn't do it.


If your car still has the original battery, I wonder if it's a warning that it's dying.

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