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Old 02-01-2019, 01:24 PM   #1
MkIII
Scooby Newbie
 
Member#: 100637
Join Date: Nov 2005
Chapter/Region: NWIC
Location: Portland, OR
Vehicle:
2002 Legacy GT
Silver Stone

Question 2002 Legacy GT - Battery/Brake Light Issue

I recently had to replace my alternator due to the old one dying after 180k miles. I used a genuine Subaru re-manufactured unit as a replacement. However, the Battery & Brake lights remain lit -- it's my understanding that these both light up when there's a charging issue in this generation of car.

Here's a random list of things I know so far:
  1. The new alternator is charging the battery based both on having it tested and the feedback from an OBD2 scanner.
  2. The OBD2 scanner found no fault codes were stored on the engine ECU.
  3. The battery is good.
  4. When I remove the 3-pin plug on the Alternator the warning lights go out.
  5. I checked the relays and fuses related to this circuit and they appear to be good. I did a continuity test on the 10A fuse for the alternator and it was fine.
  6. I recently replaced the all the smaller wedge bulbs in the cluster with LED equivalents.

Right now my suspects are the new LED wedge lamps or that somehow both the testing and the OBD2 scanner are not telling me the whole story. The test they ran is one of those units they attach to the battery, then run the car to a certain RPM, and hold it there while the testing unit does its work.

I'm hoping someone here might have some suggestions of things I might check to further diagnose and hopefully resolve the issue.

Thanks!
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Old 02-13-2019, 01:14 PM   #2
Cougar4
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Member#: 53443
Join Date: Jan 2004
Location: Anchorage, AK
Vehicle:
2001 LL Bean Outback
Winestone

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If you replaced the battery and brake warning lights with LED lights you most likely are going to have to put the filament bulbs back in place. You have proved that the trouble is with the connection to the alternator (Step4). There could be an internal problem with the alternator causing the problem. I suggest you first try a temporary test circuit using the original bulbs in place of the LEDs to see what happens with that before trying a new alternator.
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Old 02-15-2019, 03:01 PM   #3
MkIII
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Member#: 100637
Join Date: Nov 2005
Chapter/Region: NWIC
Location: Portland, OR
Vehicle:
2002 Legacy GT
Silver Stone

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Quote:
Originally Posted by Cougar4 View Post
If you replaced the battery and brake warning lights with LED lights you most likely are going to have to put the filament bulbs back in place. You have proved that the trouble is with the connection to the alternator (Step4). There could be an internal problem with the alternator causing the problem. I suggest you first try a temporary test circuit using the original bulbs in place of the LEDs to see what happens with that before trying a new alternator.
I very much appreciate your reply.

I ended up taking the car to a local shop as I was pretty frustrated with it. I wish I'd have calmed down just a little though because in the end, it was indeed the LED wedge bulb.

The shop suggested that the LED bulb in the battery warning indicator was adding too much resistance in that circuit causing the issue. Evidently it's rather sensitive. Once they replaced that one LED with a #37 incandescent everything went back to normal.
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Old 02-17-2019, 11:29 AM   #4
Cougar4
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Member#: 53443
Join Date: Jan 2004
Location: Anchorage, AK
Vehicle:
2001 LL Bean Outback
Winestone

Default

You are not the first one to have this issue happen to them. What the shop told you is correct. LEDs don't require very much current to turn them on and there is a current limiting resistor inside it that will restrict the current through the LED when it is biased on, but that also restricts the proper current needed by the alternator to allow it to work like it should. The normal bulb allows more current to flow to the exciter in order to get the windings inside the alternator charged up. Glad to hear you got it working again.
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