Battery / ABS / Brakes / CEL lights, Blown Headlamps – Alternator Failure!

fibber2fibber2 Member Posts: 3,786
edited January 2014 in Subaru

I posted this on another “Subaru Outback” board yesterday, but figured I’d place it here also. It might help someone else searching for answers.

Last week during the intense cold snap my daughter reported a few intermittent dash lights, and then last Wednesday night the car (’02 OBW, H4 auto w/112k miles) left her stranded. I got there about ¾ of an hour later expecting it to just be a weak battery (it was a few degrees above zero), but it soon became obvious that it was a lot more serious than that. The battery was deeply discharged, and even once started we had a dash full of intermittent indicators depending on RPM, and the headlamps were out. It died on the 12 mile trip home less than a mile from the house, and again at the top of my driveway. We rolled the final 500 ft downhill, and into the garage!

The headlamp filaments were obliterated (molten balls of tungsten!), an obvious sign of a severe voltage spike. I did what I could with a meter and my eyes/ears, but there was no way I was going to attempt another start for fear that if it was a voltage regulator, the last thing I wanted was a blown ECU (if we didn’t already have one). With the battery fully recharged and the key to ‘on’ most things came to life, including the fuel pump. A good sign. Grounds were all good, with millivolts separating the negative battery terminal from body and block points while under load. No big voltage dips, so no obvious signs of a short somewhere. Next stop, try a new alternator.

Rebuilt OEM (Mitsubishi 90A) units were $225 from the dealer. I found that Advance Auto had a Hitachi case brand new compatible unit for $145, and I found a $50 (off $125 or more) coupon on line. The price was certainly right, and I had the unit in my possession in less than a day (warehouse to store delivery).

Installation is pretty easy on this rig. I used a little 12v keep-alive supply to retain radio and ECU memory while working. She fired right up, but with a CEL and a bit of a lumpy idle. I checked the freeze-frame data, but it was consistent with a dying electrical system (multiple misfires, speed sensor malfunction, AF sensor failure, a short term fuel trim of 37% (!), vehicle speed of zero while under load @ 2300 RPM – your basic wacko stuff). I cleared them and she started better on the second attempt. A little more meter work indicated nothing over 14.4v, and she held 12.6v even with a heavy load. Add in $25 for a pair of H1 bulbs, and a few days of driving later it all seems to be OK. My fingers are still crossed that whatever overvoltage event did occur didn’t torture other things into a death spiral down the road.

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