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Discussion Starter #1
Hello,
I'm new to the forum, but hoping someone can help...06 Forrester , 194K miles and now has eaten 2 alternators and a battery this past year. Any help on why? I have a certified mechanic, but he has no good reason why either.
May be coincidental, but A/C works when it wants as well. Any others with this issue?
Thanks!!!
 

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2009 Legacy
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I'd check to make sure you have the battery voltage across the body of the alternator and the big fat red lead. You should also have the battery voltage on pin 2 (middle pin) of the green connector. That's the sense wire.

Pin 3 of the green connector should be open, I suspect. It is controlled by the ECM. Your car has a mechanism that can turn off the alternator by pulling that wire to ground. Other years do not.
Check the state of that wire. I don't have hard evidence to support this (because I don't have a forester and no an alternator problem) but compared the schematics of various different year of Foresters and pin three, on some, goes to a harness to go to a connector that's open. On others, it goes to the ECM.
I strongly suspect that bad alternator problems that magically just appear is related to that mechanism and mixing different year alternators.

Here's a link that describes a hack. Show that to your mechanic. I bet an easier hack would be to tie pin 3 to the state that makes the alternator charge, whichever state that is.
 

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Thanks for your reply. I have read many comments about this year having issues with the 3 wire green connector, but mine only has 2 wires in that plug. I will relay your reply to my mechanic and see what happens. Thanks again,
 

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Thanks for your reply. I have read many comments about this year having issues with the 3 wire green connector, but mine only has 2 wires in that plug. I will relay your reply to my mechanic and see what happens. Thanks again,
NP
Yours only has two connections in that plug? Here's a schematic to a 2003-2008. It shows three pins..
Alt-2 goes to the ECM.

Btw, fuses are ok, I'm sure?
526467
 

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The fuses were all good, the best I could see. Is there a certain one I should look closer at? And, yes there are three pins in the plug, but only 2 wires coming out of it, they are inside a black wire protective sleeve which then join the wiring harness. Should there be a 3rd wire coming out of the plug as well?
Thanks much,
 

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Should there be a 3rd wire coming out of the plug as well?
Thanks much,
According to the schematic I have for you year, it should have three pins so that's a little weird. The older ones had wiring like yours. My schematic is from a copy of the Subaru service manual.
Regardless of what's going on, I'm wondering whether that third pin that's currently unused on your alternator needs to be hooked into something.
Maybe the alternator that was swapped in needs that third pin hooked to a known state. It could be that Subaru thinks that leaving that pin 'float' makes no difference but it wouldn't be the first time someone screwed up thinking that.
Floating pins sometimes float to a condition that you don't want over time or when exposed to static electricity.

If you're willing and daring enough and have the tools, the following may be worth trying.
Since your alternator is thought of as bad anyway, it can't make it any worse:

  • Stick a bare wire in that unused pin going into the alternator. Rig that somehow. We'll call it a test wire
  • Put a multimeter across the battery.
  • Start the car.
  • With a test light to ground, touch that test wire and see what happens to the voltage on the multimeter.
  • If nothing happens, see what happens when you attach that wire to battery positive and touch that test wire again.
I'm suggesting making the connection to that test wire through a test light as the bulb in the light will limit the current so nothing bad should happen. Once you determine that making a connection to ground or 12V makes it work, you can just wire it to that state.

Please do report back what you or your mechanic finds.
 
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