2000 Legacy Alternator

[Rebecca B.]

I have a 2000 Legacy the check engine light keeps coming on. The last
time I took it to the dealer they said that it was the code for the
alternator and if the light came on again with the same code, I would
need a new alternator. So the light is on again, but I can't believe
that any thing so major would be wrong with my car because it runs fine
and isn't making any funny noises or anything. Is there anything else
that could cause this to happen (I recently left one of my interior
lights on for a couple of hours and I am slightly over my oil change
miles) and are there any symptoms of a bad alternator I should be
looking out for?

 

[John Rethorst]

I had just been ignoring
the light and it would come on, stay on for about three days

This isn't your question, but I think that's too long to ignore a light.

 

[Carl 1 Lucky Texan]

I have a 2000 Legacy the check engine light keeps coming on. The last
time I took it to the dealer they said that it was the code for the
alternator and if the light came on again with the same code, I would
need a new alternator. So the light is on again, but I can't believe
that any thing so major would be wrong with my car because it runs fine
and isn't making any funny noises or anything. Is there anything else
that could cause this to happen (I recently left one of my interior
lights on for a couple of hours and I am slightly over my oil change
miles) and are there any symptoms of a bad alternator I should be
looking out for?

If we had the actual code number, we might be able to advise
specifically. Do you have any receipt with a code numebr on it? My
instincts tell me that your alternator is fine - but....

Some auto parts stores (Autozone for example) will read the code, and
sometimes clear a code (might need a $5 tip in some states...wink...wink)

There are many things that will turn the light on, from not tightening
the gas cap well enough (a dozen or more 'clicks' may be required) to
bad/lazy sensors (you may be due for a front oxygen sensor - they get
'lazy' intermittent in their old age) to TPS MAF failure or a simple
misfire from old plugs or bad plug wires. If your are uncomfortable with
the light on, either have the code read and post here, or find a good
local mechanic. Personally, I might try a different one from the last
place.

Carl

 

[Rebecca B.]

If we had the actual code number, we might be able to advise

specifically. Do you have any receipt with a code numebr on it? My
instincts tell me that your alternator is fine - but....

I do have the code on a receipt somewhere, but it is at home and I am
at work, I will look for it when I get home.

A little bit more background on the situation, I had just been ignoring
the light and it would come on, stay on for about three days and then
go off, the car would continue to run fine. Then in September, the
third time this happened, I took it to a local independent car fixer
and he told me that it was the front oxygen censor and that there was a
recall on this sensor and that I should take it to the dealer to have
them replace it. He even printed information out for me about this
recall. So I took my car to the dealer, the dealer told me it was the
alternator and since they didn't know the history of the car, they were
just going to clear the code and if the light came on again to come
back.

So, now I don't know who to believe, they both gave me the same code. I
have an appointment at a third car place in about a week and a half to
have new tires put on, maybe I will just wait and have them look at it.

 

[mulder]

I do have the code on a receipt somewhere, but it is at home and I am
at work, I will look for it when I get home.

A little bit more background on the situation, I had just been ignoring
the light and it would come on, stay on for about three days and then
go off, the car would continue to run fine. Then in September, the
third time this happened, I took it to a local independent car fixer
and he told me that it was the front oxygen censor and that there was a
recall on this sensor and that I should take it to the dealer to have
them replace it. He even printed information out for me about this
recall. So I took my car to the dealer, the dealer told me it was the
alternator and since they didn't know the history of the car, they were
just going to clear the code and if the light came on again to come
back.

So, now I don't know who to believe, they both gave me the same code. I
have an appointment at a third car place in about a week and a half to
have new tires put on, maybe I will just wait and have them look at it.

There is no code for a bad alternator. If it fails it may (but won't
always) cause the "battery" warning light on the dash to come on.
Sometimes they go bad in a way that does not turn the light on.
A shop with the proper diagnostic equipment can fully evaluate your
electrical system and determine the condition of the alternator and
battery.
Autozone will read codes for free, you should get them to do so and
post the actual Pxxxx code here. Just stating that it's for an oxygen
sensor is not sufficient to narrow the problem down, as there are
quite a few different codes that are 02-sensor related. Even with the
code however, there can be multiple causes. We can sit here on the
Internet and speculate, but only a tech at a dealer or shop with their
hands on the car can find the actual problem.
So somebody along the line here is feeding you BS.

 

[Jim L]

The Schucks here in Redmond, WA will read codes for free also.....Jim

 

[Rebecca B.]

So, I'm a big liar. I went back and looked at my paperwork and it is
the CATALYTIC CONVERTER that the dealer told me the code was for. The
code by the way is P0420.

So my original post should read:

 

[mulder]

So, I'm a big liar. I went back and looked at my paperwork and it is
the CATALYTIC CONVERTER that the dealer told me the code was for. The
code by the way is P0420.

So my original post should read:

Ok, that makes more sense now. If you have less than 80K miles on the
car the catalytic converter is covered under the Federal emissions
warranty which is 8/80, so your dealer should replace the converter
for you for free.
There may not be any symptoms as long as the converter is not clogged.
When that code is set it indicates that the engine computer has
determined that the catalyst is no longer performing effectively.

 

[Carl 1 Lucky Texan]

Ok, that makes more sense now. If you have less than 80K miles on the
car the catalytic converter is covered under the Federal emissions
warranty which is 8/80, so your dealer should replace the converter
for you for free.
There may not be any symptoms as long as the converter is not clogged.
When that code is set it indicates that the engine computer has
determined that the catalyst is no longer performing effectively.

The only way the ECU can interpret the possibility of a bad cat conv is
by comparing the upstream lambda sensor to the after-cat sensor. It is
MOST likely you have a bad/lazy sensor. Have the front O2 sensor changed
(OEM is prefered - try www.subarugenuineparts.com ) and the code
cleared. If it returns, perhaps have the rear sensor changed. The price
of those repairs will still likely be 1/5 the cost of a converter.
Converters CAN go bad of course - but usually there are noticeable
performance problems or other symptoms.

And don't use that first shop unless they can convince you the actually
flow tested the converter.

Carl

 

[mulder]

The only way the ECU can interpret the possibility of a bad cat conv is
by comparing the upstream lambda sensor to the after-cat sensor. It is
MOST likely you have a bad/lazy sensor. Have the front O2 sensor changed
(OEM is prefered - try www.subarugenuineparts.com ) and the code
cleared. If it returns, perhaps have the rear sensor changed. The price
of those repairs will still likely be 1/5 the cost of a converter.
Converters CAN go bad of course - but usually there are noticeable
performance problems or other symptoms.

And don't use that first shop unless they can convince you the actually
flow tested the converter.

Carl

While Carl MAY be right, generally if one of the 02 sensors is bad it
will set additional codes that are specific to a bad sensor. This is
true for the front sensor particularly, since it controls the engine
air/fuel ratio and is carefully monitored by the ECU.
Since you have already had a dealer confirm that the converter is bad
you should ask for a free replacement under the 8/80 warranty as I
mentioned, as long as your car does indeed have less than 80K.