alternator and oxegyn sensor

Hi
I just had my third alternator since january fail on my 2002 outback. Everytime the alternator starts to fail, the check engine light goes on
and I am told that the o2 sensor needs to be replaced.
it seems too much a coincidence that these failures happened all three times the alternator goes. Is it possible that it is a false diagnostic based on the sensor not getting enough power from the alternator...or could it be that the screwy power it is receiving from the faulty alternator is damaging the sensor?
Mike Cardeiro
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Hey Mike, [ evL ] here...
This has been my experience whether it is of help or not...
From what I have read in my 98' OBW manual when the check engine light comes on it only means that something is wrong with the emissions. Surprising I thought. When it seems more important to me to be notified if one is low on oil or if the timing belt is about to break. If you know what I mean.
Also, and more to your issue, I will say this; when the alternator is "gone" or is "going out" all kinds of weird things happen. When mine went out for the first time all the gauges went berserk, nothing worked right. In fact it really seemed that the car was possessed. Being used to older vehicles I couldn't believe what was going on, only to find out that it was the alternator.
By the way, my "check engine light" never came on when my alternator was going out. I am pretty sure that light is an emission only thing. Of course what do I know right?
I will say this, if you have had three alternators since January then something is obviously "squashing" your alternator because I doubt your buying inferior equipment each time.
Hell, try replacing the O2 sensor. Or try getting an alternator from another source and get one that is not rebuilt.
Like I say; you mentioned, "diagnostic based on the sensor not getting enough power from the alternator", well if that was the case your tack, speed-o, cruse-control, and much more would be failing if it was the alternator.
I probably haven't helped a bit but defiantly curious about replacement of an alternator three times since January. That's just not right.
Take care buddy, I'll be watching this post. And good luck.
[ evL ]

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[ evL ] wrote:

yes it is f'ed up. The first replacement lasted from january until July, the second one lasted a week, and I am keeping my fingers crossed on the third one!

Them oxegyn sensors aint cheap...I hate to keep replacing them. According to the shop that did the alternator the only way to get a new alternator is to buy a new car...nobody will sell you anything but a rebuit one; and they said that it is total hit or miss as to whether it is going to last, he said out of five rebuilt alts three will fail.
Mike Cardeiro
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3 out of 5 seems awfully high, I've had a number of rebuilt starters/alternators and only ever heard of 2 rebuilt starter problems and 1 alternaotr problem that friends have had over the years. I do think the ground strap or wire from the motor to chassis needs to be verified, as someone posted earlier. I can't see the O2 sensor going from a bad alternator, the sensor gives a weak voltage signal (.1 to .8 volt or thereabouts) when it is heated by the exhaust, which is read by the engine computer. A bad alternator has no effect on the sensor output, it's the heat that generates the voltage, and the oxygen content that varies the amount.
Ed B
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Reading all the posts made me think may be there is a connection between the O2 sensor and alternator. Both need to be grounded to function. I believe the sensor is grounded through the exhaust system, but there has to be a grounding wire somewhere to finish the circuit. The person that suggested a grounding strap is probably on the right track.
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When the alternator is failing reduced voltage can result in many other strange problems which aren't permanent. I agree with the comments re grounding straps, in fact I'd remove and reseat all electrical connectors associated with the alternator and battery. Frequent alternator problems indicate some other problem causing it.
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mcardeiro wrote:
Ouch! I hope you get a warranty on reco items over there. I've usually get 12 months on reco alternators in Aus and I've only ever had one warrnaty claim. Now Lucas generators ..... there's another story!
Yep. Check earthing. Maybe something's finding an easier path to ground via the alternator. Anyone know if a dodgy regulator/rectifier could cause anything like this? Cheers
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I once had an old car that was eating generators. Until an 'old timer' said it was due to bad ground from engine to chassis. A ground strap fixed everything. maybe you have some corroded ground connections/wires?
Carl
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thanks to all. I sure wish I knew what a ground strap was and how to check it out...oh well, I gues I will be giving more money to the mechanic man!
Mike Cardeiro
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mcardeiro wrote:

Just before you do though .... when you've got an idle moment, pop the hood and take a look at the battery. It's got a +ve and a -ve terminal. The -ve one should have a cable coming from it that bolts securely to the bodywork somewhere. That's a ground for the battery. Front and back lights, engines, stuff in the dash, etc, usually have thinner or thicker versions of the same thing. Giveaway is they run direct to the bodywork somewhere and they're often black. If something that's giving you a problem has one that's corroded, loose, or broken, fixing it up is often a simple solution to a frustrating electrical problem. Cheers
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