2008 Legacy 3.0 liter Charging Issues

[Dave Allen]

The car in question has already had 2 alternators and batteries installed. After I started getting involved with it, I found that there was no apply voltage coming from the ECU to the alternator. (Only .250V) The charging output is non-existent. If I physically feed in a 3 volt signal, the alternator tarts putting out 14.56 V as it should. No battery light on during the no charging phase. But the bulb proves out during key on. No codes.

So my question is this.....where does the ECU get it's sense of "vehicle load" to enable it to feed voltage to the alternator for charging? Initially it was thought the ECU was just bad, as nothing would change the trigger voltage for the alternator. So, new ECU, but still the same problem.

All fuses are good, new battery, new (aftermarket) alternator, new ECU.

i noticed a procedure used to trick the ECU into constantly charging. I was wondering if it would work for this vehicle?

Any ideas on where to go from here?

 

Edited October 3, 2018 by Dave Allen
Added sentence.

[idosubaru]

Hopefully someone will chime in but I would consult the FSM otherwise, it should have a diagnostic tree to check that somewhere. 

[1 Lucky Texan]

typical parts store rebuilts are often wrongly stocked/buoilt for the 3.0 motors. Sure you are getting proper alts? I'm CERTAINLY no expert, but the 3.0 unit may have higher impedance on the 'field' input wire and those  (possibly) incorrect alts are sinking too much current from the ECU's control output.

Might be worth trying a used alt or, if you still have your original, have a local rebuilder go thru it for you.

 

there's also DBW or maniac electric or ???

Edited October 3, 2018 by 1 Lucky Texan

[idosubaru]

Were the symptoms of the first failed alternator identical to what you have now or you're uncertain? 

Aftermarket is a good point, there are reports of H6 aftermarket alternator issues.  if you can get a used OEM one, try it out.