alternator and oxegyn sensor

[mcardeiro]

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

 

[[ evL ]]

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 ]

 

[Carl 1 Lucky Texan]

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

 

[mcardeiro]

[ evL ] wrote:

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.

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!

Hell, try replacing the O2 sensor. Or try
getting an alternator from another source and
get one that is not rebuilt.

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

 

[ed]

[ evL ] wrote:

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.

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!

Hell, try replacing the O2 sensor. Or try
getting an alternator from another source and
get one that is not rebuilt.

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

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

 

[johninKY]

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.

 

[Moon Guy]

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.

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.

 

[hippo]

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

 

[mcardeiro]

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

 

[hippo]

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

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