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Thread: 1999 legacy gt weird idle voltage

  1. #1

    1999 legacy gt weird idle voltage

    Hello. I have a 1999 Subaru Legacy gt 5mt and when the car returns to idle at stop lights and what not there is a very noticeable dimming of all the lights on the car. No ligh turn on on the dash but after checking the voltage of the battery the altonator only puts out 13.0 volts at idle. Once’s the engine leaves idle the voltage returns to 14.0 volts. I have a new altonator so I’m wondering if this is normal or if the altonator is going out again. From what I’ve read it could also be a bad ground but I have no idea where to check for that. Some help would be greatly appreciated.

  2. #2
    SLi Lurker Sub-Goon's Avatar
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    Look for any ground connection between the engine/trans and body. Clean off all oil/grease, scuff all the components with sandpaper or wire brush. As you reassemble the connections, use Dielectric Grease. You could also replace any OEM grounds with 4 gauge welding wire & eyelets from Home Depot or Stereo Install shop.

    If that doesnt get the alternator output a bit higher then pull the alternator and take it to an Auto Electric shop to have them check it out.

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    "FNG" Kamion's Avatar
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    13 V at idle is completely normal.
    Subaru Legacy GL EJ20 (BH, year 2002)

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    "FNG"
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    Is it normal for the lights to dim at idle?

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    Mine Usually Dims as well and I have a 96 Legacy LS, but not sure if it’s “normal”

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    "FNG" Kamion's Avatar
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    Sorry I was wrong.
    Even on Idle voltage should not go under 14 V. I tested it on mine, and it never goes under, even on idle it stays up.
    It goes under 14 V only if I switch on all the electricity users (heated everything, all lights...)
    Subaru Legacy GL EJ20 (BH, year 2002)

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