neil_ski Posted July 13, 2006 Share Posted July 13, 2006 Hi all New to the forum. My lady's nice 2001 Legacy has had some issues. The battery and alternator light turned on while she was driving. I checked voltage across the battery and sure enough, it wasn't charging. It showed about 11 volts while running. I took the alt to a rebuild shop, got it back, and at first it worked OK. (I think) I didn't check the voltage after I put it in. The battery showed 12 volts before startup, and it cranked hard so I didn't think it needed to be charged. It fired up right away and no warning light turned on. I drove it for 5 minutes and all seemed fine. The next day, my lady calls me and says that the battery light and brake light are back on. I check it out, and it's not charging. The battery terminals needed some cleaning, I cleaned them and it made no difference. My installation looked ok. No screw ups. I'm at a loss here. What could have happened? I'm guessing that the shop did a bad job. But is there anything else that could cause this? I read a lot of posts in the forum and found out that said the ECM controls the field of the alternator. Could this do anything? The car was involved in a flood last year. They replaced some computer board. Not sure which. I hope stuff isn't all coroded up! Thanks for your help Neil Quote Link to comment Share on other sites More sharing options...
firstwagon Posted July 13, 2006 Share Posted July 13, 2006 There's almost nothing a car's electrical system can do in one day to wreck an alternator. If it failed after one day then something they replaced on the rebuild was on the short end of the bathtub curve. Take it back to the rebuild shop and have redo it or replace it. Quote Link to comment Share on other sites More sharing options...
Setright Posted July 13, 2006 Share Posted July 13, 2006 Brake light and battery light on? Diode bridge/ rectifier in the alternator is bad. Not your car's fault. Quote Link to comment Share on other sites More sharing options...
benebob Posted July 13, 2006 Share Posted July 13, 2006 A bad battery can kill an alternator in a day for sure. Did you charge the battery up when you replaced the alternator as I'm sure it had been drained down. My guess is at 12 volts (Should be 13.2) you have a bad cell probably which means the alt was working overtime trying to meet the needs of the battery and burned itself out. Quote Link to comment Share on other sites More sharing options...
edrach Posted July 13, 2006 Share Posted July 13, 2006 Benebob is right about a faulty battery causing alternator failure. An open circuit (internal or bad connectors) in the battery while the car is running can wipe a good alternator almost instantly. In any event go back to the rebuild shop and explain the situation. A quality shop will warrantee their work; they also have the ability to check your electrical system to make sure the alternator didn't fail due to external problems. Quote Link to comment Share on other sites More sharing options...
nipper Posted July 13, 2006 Share Posted July 13, 2006 you cant check a battery by voltage alone. You need to load test it. a bad battery will wipe out an altenator. nipper Quote Link to comment Share on other sites More sharing options...
ericem Posted July 13, 2006 Share Posted July 13, 2006 Usually when my alt dies i change both the battery and then i buy a brand new alt. This way you can be safe to know that all the cells in the battery are full. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted July 13, 2006 Share Posted July 13, 2006 alt and batt often fail in pairs. i see it all the time when friends/family call me with problems. off the top of my head i'd say 30-50% of the time they have a bad batt or alt, they are both bad or the other fails in a matter of months. i'm not an electrical pro but what i've seen supports what these guys are saying. i'd have the batt tested or heck if it's old at all might be best to replace it, they aren't that expensive. if your connections were dirty/corroded the battery may have a very slow leak in it as well, might be another sign that replacement is in good order. with a good alt, battery and tight connections there will be little to no corrossion at the terminals. Quote Link to comment Share on other sites More sharing options...
benebob Posted July 13, 2006 Share Posted July 13, 2006 Benebob is right about a faulty battery causing alternator failure. An open circuit (internal or bad connectors) in the battery while the car is running can wipe a good alternator almost instantly. In any event go back to the rebuild shop and explain the situation. A quality shop will warrantee their work; they also have the ability to check your electrical system to make sure the alternator didn't fail due to external problems. Even if it is your batteries fault like edrach says it is most likely the only damage would be the diode that was mentioned first. I doubt any shop would charge more than parts and labor to replace that one part on a good will basis as the rest of the alt should be tip top. Quote Link to comment Share on other sites More sharing options...
benebob Posted July 13, 2006 Share Posted July 13, 2006 Benebob is right about a faulty battery causing alternator failure. An open circuit (internal or bad connectors) in the battery while the car is running can wipe a good alternator almost instantly. In any event go back to the rebuild shop and explain the situation. A quality shop will warrantee their work; they also have the ability to check your electrical system to make sure the alternator didn't fail due to external problems. Even if it is your batteries fault like edrach says it is most likely the only damage would be the diode that was mentioned first. I doubt any shop would charge more than parts and labor to replace that one part on a good will basis as the rest of the alt should be tip top. Quote Link to comment Share on other sites More sharing options...
neil_ski Posted July 13, 2006 Author Share Posted July 13, 2006 Even if it is your batteries fault like edrach says it is most likely the only damage would be the diode that was mentioned first. I doubt any shop would charge more than parts and labor to replace that one part on a good will basis as the rest of the alt should be tip top. Wow! Thanks for the replies! I took it back at lunch time. He tested it and said that it seemed to be charging but one of the input/outputs from the plug wasn't working right. He called someone to pick his brain, and that someone is going to call someone else. He's also having his employ tear it down and inspect it. He just called and said the regulator died again. They're going to overnight a part so I can get it back by tomorrow. Good service at least! As for the battery, It's old, but it kept her car running to work, and back to home after the warning lights turned on. I don't think a defective battery could do that. Right? Still, I think I will have it tested. Hope this solves it. She loves that car! And the AWD is really nice on the icy snowy Minneeesota roads. ha ha Thanks! Quote Link to comment Share on other sites More sharing options...
ericem Posted July 13, 2006 Share Posted July 13, 2006 Yup subarus are the only car i would buy, but still i must suggest u replace that battery it wont hurt u know. Quote Link to comment Share on other sites More sharing options...
benebob Posted July 13, 2006 Share Posted July 13, 2006 As for the battery, It's old, but it kept her car running to work, and back to home after the warning lights turned on. I don't think a defective battery could do that. Right? Still, I think I will have it tested. Yes, a defective batter can do that. Most cars don't need all the voltage to start it and make it run at all. Take it to Sears, Autozone, etc and have it charged and tested unless you have the equipment at home to do so. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted July 13, 2006 Share Posted July 13, 2006 yes a bad battery can still "run" and start a vehicle but cause other problems. Quote Link to comment Share on other sites More sharing options...
nipper Posted July 13, 2006 Share Posted July 13, 2006 yes a bad battery can still "run" and start a vehicle but cause other problems. a battery can run a car for about 20 miles with no accessories on. (i think even the owner manual tells you that have to double check). But running the battery down when its old will damage the battery. The battery will self recharge to a degree given enough time. If the battery is over 5 years old you may want to shop for a battery too. nipper Quote Link to comment Share on other sites More sharing options...
Strakes Posted July 13, 2006 Share Posted July 13, 2006 I had my alternator crap out on me, and then my battery started acting funny within a few days. The battery had an internal short that showed up randomly, eluding tests. Towing charge next time your wife is stranded: $50 Wife's anger avoided by buying a new battery now: priceless Quote Link to comment Share on other sites More sharing options...
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