02 legacy misfire and 02 codes

[ray]

Just bought a used 02 Legacy L 2.5/5spd.

Started idling rough, and check engine came on.
Dumped codes, got a p0130 and a p0171. Cleared them, and then 2 days
later, hot p0301-4 (misfires in all 4 cylinders.)

I'm going to see if there's any warranty left, but I suspect I'm on my
own...

plugs and wires were apparently just done... because of the same thing.

the one thing my autotap did show was the long term fuel trim was -23%
IIRC, which is why the p0171...

I don't yet have a shop manual, so I'm looking for some assistance on
where to start - 02 sensor? Which one(s)? I haven't even looked under
the car yet, so does the 2.5 have one 02 per bank or one for both banks?

The car runs fine once you're up to speed, but definitely idles like
crap. Nothing obviously broken/unhooked under the hood, but I'll be
having a more in depth look tomorrow.

One thing I read talked about exhaust leaks upstream from the 02 sensor
- this car has a new clutch, is it possible the mechanic who did the
clutch messed something up?

Grrrr... car drives nice, but I'm busy right now, and I was hoping it
would be a nice reliable winter car so I could finally put the wife's
Beretta out to pasture.

(and if you're wondering why I bought it when it's got some mechanical
history, it's because the body and interior are almost perfect - I can
fix mechanical, but rust is evil and apparently every other Subaru owner
has dogs. Big smelly dogs that eat parts of the interior. Plugs and 02
sensors are cheap compared to new dash pads without bite marks.)


Ray

 

[Carl 1 Lucky Texan]

Just bought a used 02 Legacy L 2.5/5spd.

Started idling rough, and check engine came on.
Dumped codes, got a p0130 and a p0171. Cleared them, and then 2 days
later, hot p0301-4 (misfires in all 4 cylinders.)

I'm going to see if there's any warranty left, but I suspect I'm on my
own...

plugs and wires were apparently just done... because of the same thing.

the one thing my autotap did show was the long term fuel trim was -23%
IIRC, which is why the p0171...

I don't yet have a shop manual, so I'm looking for some assistance on
where to start - 02 sensor? Which one(s)? I haven't even looked under
the car yet, so does the 2.5 have one 02 per bank or one for both banks?

The car runs fine once you're up to speed, but definitely idles like
crap. Nothing obviously broken/unhooked under the hood, but I'll be
having a more in depth look tomorrow.

One thing I read talked about exhaust leaks upstream from the 02 sensor
- this car has a new clutch, is it possible the mechanic who did the
clutch messed something up?

Grrrr... car drives nice, but I'm busy right now, and I was hoping it
would be a nice reliable winter car so I could finally put the wife's
Beretta out to pasture.

(and if you're wondering why I bought it when it's got some mechanical
history, it's because the body and interior are almost perfect - I can
fix mechanical, but rust is evil and apparently every other Subaru owner
has dogs. Big smelly dogs that eat parts of the interior. Plugs and 02
sensors are cheap compared to new dash pads without bite marks.)


Ray

Assuming the car has typical mileage - yeah, front O2 is a candidate for
being lazy. I wouldn't rule out something as simple as a vacuum leak
(since work has been done, a hose may be missing or cracked) all the way
up to a MAF sensor ($$$ unless carefully cleaning the element doesn't
fix it).

Does it idle/start differently cold than hot? Engine Temp Sensors (not
gauge sender) can confuse the ECU if bad.

hopefully someone will chime in with more experience.

Carl

 

[ray]

Assuming the car has typical mileage - yeah, front O2 is a candidate for
being lazy. I wouldn't rule out something as simple as a vacuum leak
(since work has been done, a hose may be missing or cracked) all the way
up to a MAF sensor ($$$ unless carefully cleaning the element doesn't
fix it).

Does it idle/start differently cold than hot? Engine Temp Sensors (not
gauge sender) can confuse the ECU if bad.

hopefully someone will chime in with more experience.

Carl

it runs fine when cold, but starts to idle rough when warm.
always starts fine.
the idle is around 750, then around 650, then around 500, then up to
1000, then back to 750...

 

[Carl 1 Lucky Texan]

it runs fine when cold, but starts to idle rough when warm.
always starts fine.
the idle is around 750, then around 650, then around 500, then up to
1000, then back to 750...

The Engine Temp Sensor may be bad, effectively keeping the 'choke' on.
That would explain good idling/running conditions when cold - poor
idling/running when warm. But it may not explain all the codes. I
suppose there is a slim possibility of 2 issues occuring at once, say-
lazy O2 and bad ETS.

a haynes or other manual may have voltmeter tests you could perform.

Carl

 

[ray]

The Engine Temp Sensor may be bad, effectively keeping the 'choke' on.
That would explain good idling/running conditions when cold - poor
idling/running when warm. But it may not explain all the codes. I
suppose there is a slim possibility of 2 issues occuring at once, say-
lazy O2 and bad ETS.

a haynes or other manual may have voltmeter tests you could perform.

Carl

temp sensor looks ok... I sat in the car today with the autotap plugged
in... I'm really leaning towards a "worn" 02 sensor... 90% of the time
it's showing 25mV, when what info I have says it should be showing
300-600 as normal.

The long term fuel trim IIRC was -23, which I believe is what starts
this whole process - the PCM is convinced it's lean based on the 02
sensor, so it adds more gas... but it's still showing lean.

I'm just not yet ready to spend $300 on a non-returnable 02 sensor.

 

[Lawrence Glickman]

temp sensor looks ok... I sat in the car today with the autotap plugged
in... I'm really leaning towards a "worn" 02 sensor... 90% of the time
it's showing 25mV, when what info I have says it should be showing
300-600 as normal.

The long term fuel trim IIRC was -23, which I believe is what starts
this whole process - the PCM is convinced it's lean based on the 02
sensor, so it adds more gas... but it's still showing lean.

I'm just not yet ready to spend $300 on a non-returnable 02 sensor.

What is this baloney. Pull the O2 sensor and CLEAN IT. Then
reinstall it and keep the $300 for something else.

FYI, here are my scan numbers for my 03 Vulcan V6

02 sensor bank 1 sensor 1 0.9,0.1,0.8,0.1
short term air/fuel correction ratio bank 1 -2.3,1.6,3.1,0
02 sensor bank 1 sensor 2 0.845,0.840,0.865,0.870

02 sensor bank 2 sensor 1 0.88,0.1
short term air/fuel correction ratio bank 2 -2.3,0.8,1.6,2.1,3.9,0
02 sensor bank 2 sensor 2 0.83,0,0.825,0.830


IOW, downstream sensor fires ONCE for every 127 toggles of the
upstream sensor, which toggles at about once ever 0.5 seconds. That's
the way it is SUPPOSED to work. And the voltage goes from 0.1 low to
0.87 high.

What are you talking about with this 25 millivolts. That's 0.025.
DEAD. If it is downstream, wait for it to toggle. If it is upstream,
you should see it toggle about 2 times/second.

Lg

 

[Comboverfish]

temp sensor looks ok... I sat in the car today with the autotap plugged
in... I'm really leaning towards a "worn" 02 sensor... 90% of the time
it's showing 25mV, when what info I have says it should be showing
300-600 as normal.

It is likely you are correct about the front "O2" sensor being faulty
because it is a common cause for code P0130 on your vehicle . The
actual component is called an air/fuel ratio sensor, and works
differently than an O2 sensor, though it looks the same and does
basically the same thing only with much more resolution. The big
problem is that you are using a generic scantool device which most
likely doesn't display the A/F sensor reading properly.

The quickest, easiest way to test an A/F sensor is with the appropriate
scantool due to the unorthodox signal(s) they generate. The ECM
measures A/F current direction, timing and amplitude and creates an
output in the diagnostic serial data stream. That is then descrambled
by the scantool (if capable) and reported as 0-5 volts in most cases.
5 volts is max lean and 0 volts is max rich, the opposite of O2 sensor
operation.

Your scantool may be reporting it correctly at .025 volts, who knows...
Some expensive multipurpose scanners don't get it right. Some factory
scanners have had problems reporting A/F sensors as well.

Point is, you should feel fairly confident that if you have a P0130
then you need one.

The long term fuel trim IIRC was -23, which I believe is what starts
this whole process - the PCM is convinced it's lean based on the 02
sensor, so it adds more gas... but it's still showing lean.

Minus 23% fuel trim means the ECM is taking away 23% fuel mass
(shortening the injectors' durations). The ECM may very well be taking
away fuel because the A/F sensor is falsly reporting rich. Remember
low volts = rich on your B1S1 sensor.

I'm just not yet ready to spend $300 on a non-returnable 02 sensor.

A/F sensors are spendy, but if you get one, do get one at the dealer as
they have been updated for this very reason. I don't think there are
any bargains to be had in the aftermarket on these as of yet, but you
may want to check into the Nippon Denso brand if you refuse to go
dealer. They have a cheaper line of the more popular sensors; don't
know if they offer this application. Anyway they are a solid quality
line that you can trust unlike most craptermarket 'bargains' out there.

Toyota MDT in MO

 

[Carl 1 Lucky Texan]

temp sensor looks ok... I sat in the car today with the autotap plugged
in... I'm really leaning towards a "worn" 02 sensor... 90% of the time
it's showing 25mV, when what info I have says it should be showing
300-600 as normal.

The long term fuel trim IIRC was -23, which I believe is what starts
this whole process - the PCM is convinced it's lean based on the 02
sensor, so it adds more gas... but it's still showing lean.

I'm just not yet ready to spend $300 on a non-returnable 02 sensor.

Ray, get a price from jamie (www.subiegal.com) who works for chaplin
(www.subarugenuineparts.com) . Even if you don't buy one from her, try
to make the local dealership match her price. If you have more than
60-80K on the car, the lambda sensor is past midlife anyway and it may
solve the problem. Some folks do report problems with aftermarket
sensors - even Bosch.

Carl

 

[Lawrence Glickman]

Ray, get a price from jamie (www.subiegal.com) who works for chaplin
(www.subarugenuineparts.com) . Even if you don't buy one from her, try
to make the local dealership match her price. If you have more than
60-80K on the car, the lambda sensor is past midlife anyway and it may
solve the problem. Some folks do report problems with aftermarket
sensors - even Bosch.

Carl

Carl, unless this is a SURE THING, nobody spends $300 on a guess.
Somebody better KNOW for certain that part is defective before they
toss that kind of money away.

100% certain that is the cause of the problem. Or, I could say, WTF,
it isn't _my_ money, why should I care?

Lg

 

[Carl 1 Lucky Texan]

Carl, unless this is a SURE THING, nobody spends $300 on a guess.
Somebody better KNOW for certain that part is defective before they
toss that kind of money away.

100% certain that is the cause of the problem. Or, I could say, WTF,
it isn't _my_ money, why should I care?

Lg

OK, if he can't diagnose it himself, how much will that cost? Those
funds could be used to buy a sensor right? And we're pretty sure the one
he has is what - half 'used up' ?

And the part might not be $300 .

I dunno - it's an option. Is it ideal? probably not.

Carl

 

[Lawrence Glickman]

OK, if he can't diagnose it himself, how much will that cost? Those
funds could be used to buy a sensor right? And we're pretty sure the one
he has is what - half 'used up' ?

And the part might not be $300 .

I dunno - it's an option. Is it ideal? probably not.

Carl

Maybe rollingviolation is a Rich Man. But to me, $300 might as well
be one million dollars. I don't want to see him make a mistake.

I don't know the man, never seen him, never will, but I don't want him
to make a mistake with *that kind* of money. It would bother me at
the moral and ethical level to have _suggested_ that was going to fix
his problem if it did not fix his problem, and he was out big cash,
and still handn't a clue.

So, =he= makes me nervous. The situation makes me nervous.
Comboverfish says it is hard with _his_ kind of sensor to make an
accurate diagnosis. He says rv has an air/fuel sensor. says it's
"LIKE" an O2 sensor, but not the same. balls. Says it's more
accurate than an O2 sensor, more expensive, harder to read with a
scanner, etc etc. BALLS.

It could be a bad connection ( corroded electrical connection ) to the
sensor, and not the sensor itself. Now we're supposed to diagnose
this sight unseen? I say, if there is _another_ one just like it in
the car, swap it with the known good one. See what happens. If the
problem switches from BANK ONE TO BANK TWO, or vice/versa. That would
be pretty good evidence.

Lg

 

[Carl 1 Lucky Texan]

OK, if he can't diagnose it himself, how much will that cost? Those
funds could be used to buy a sensor right? And we're pretty sure the one
he has is what - half 'used up' ?

And the part might not be $300 .

I dunno - it's an option. Is it ideal? probably not.

Carl

A front O2 sensor from; https://www.subarugenuineparts.com/oe_parts_cat.html

appears to be under $100 before shipping.

fyi

Carl

 

[Carl 1 Lucky Texan]

Maybe rollingviolation is a Rich Man. But to me, $300 might as well
be one million dollars. I don't want to see him make a mistake.

I don't know the man, never seen him, never will, but I don't want him
to make a mistake with *that kind* of money. It would bother me at
the moral and ethical level to have _suggested_ that was going to fix
his problem if it did not fix his problem, and he was out big cash,
and still handn't a clue.

So, =he= makes me nervous. The situation makes me nervous.
Comboverfish says it is hard with _his_ kind of sensor to make an
accurate diagnosis. He says rv has an air/fuel sensor. says it's
"LIKE" an O2 sensor, but not the same. balls. Says it's more
accurate than an O2 sensor, more expensive, harder to read with a
scanner, etc etc. BALLS.

It could be a bad connection ( corroded electrical connection ) to the
sensor, and not the sensor itself. Now we're supposed to diagnose
this sight unseen? I say, if there is _another_ one just like it in
the car, swap it with the known good one. See what happens. If the
problem switches from BANK ONE TO BANK TWO, or vice/versa. That would
be pretty good evidence.

Lg

The OBDII system considers all 4 cyl. as 'bank one' even though our
soobs have 2 banks.
An analog (and maybe some digitals?) voltmeter 'should' show the
switching of the lambda sensor mentioned.

I dunno. His car is broken, not much to be gained by not repairing it.
One could argue that the time conversing with us would be better spent
raking up his neighbors leaves for $ to buy a diagnosis from a good
mechanic.

Carl

 

[Lawrence Glickman]

A front O2 sensor from; https://www.subarugenuineparts.com/oe_parts_cat.html

appears to be under $100 before shipping.

fyi

Carl

the fish says it isn't an O2 sensor, but rather an air/fuel sensor.
"Like" an O2 sensor, but not an O2 sensor.

the fish does this for a living. maybe he knows something we don't.

Lg

 

[Comboverfish]

The OBDII system considers all 4 cyl. as 'bank one' even though our
soobs have 2 banks.
An analog (and maybe some digitals?) voltmeter 'should' show the
switching of the lambda sensor mentioned.

I dunno. His car is broken, not much to be gained by not repairing it.
One could argue that the time conversing with us would be better spent
raking up his neighbors leaves for $ to buy a diagnosis from a good
mechanic.

Carl,
Indeed it seems that the part is not too expensive. I would guess that
the OP meant $300 installed. I checked and the standard flat rate
charge is 1.5 hours. That would put the dealer part and labor right
inline with $300. Many A/F ratio sensors are big$ but this one isn't
too bad. It's a zirconium oxide design with a lower current output and
range than the big boys I am used to seeing. This looks like an
excellent DIY job to save the OP some labor, unless the sensor is
frozen in the converter. That would be bad...

Toyota MDT in MO

 

[Carl 1 Lucky Texan]

Carl 1 Lucky Texan wrote:




Carl,
Indeed it seems that the part is not too expensive. I would guess that
the OP meant $300 installed. I checked and the standard flat rate
charge is 1.5 hours. That would put the dealer part and labor right
inline with $300. Many A/F ratio sensors are big$ but this one isn't
too bad. It's a zirconium oxide design with a lower current output and
range than the big boys I am used to seeing. This looks like an
excellent DIY job to save the OP some labor, unless the sensor is
frozen in the converter. That would be bad...

Toyota MDT in MO

If the price is as quoted from a 'competent' mech. ,then the concern
about it being 'wasted' $ due to mistaken diagnosis is misplaced.

And, yeah, start soaking it in PB Blaster now and for a few days, and
try to work it out while the exhaust is still warm! That low voltage
reading is a little disconcerting - I suppose the wiring or a conn.
COULD be bad... but again, it's on the shop if he's farming it out.

Carl

 

[Ray]

What is this baloney. Pull the O2 sensor and CLEAN IT. Then
reinstall it and keep the $300 for something else.

How do you clean it?

And no, it's not switching at all. I occasionally saw 850mV then it
immediately goes back to 25.

I'm still wondering if something was unplugged and fubared when the
clutch was changed before I bought the car.

(short version -> used car, test drove it in sept, clutch was smoked,
they fixed, I drove again, but we couldn't agree on price so I walked,
they dropped the price by $1000 because it sat for a month, I bought it,
the CEL came on on the drive home. They're going to fix it, but they're
just a used car lot with a mechanic for hire, and I'm not sure how much
I trust them to fix it right, but I'm a Subaru virgin and don't yet have
a shop manual, so I'm kinda winging it based on my Firebird's shop
manual, my diy-er skills, and my gut feel. But the car goes in
tomorrow, so maybe they'll fix it. But I'm not convinced they will so
I'm making "plan b")

Ray

 

[Ray]

Minus 23% fuel trim means the ECM is taking away 23% fuel mass
(shortening the injectors' durations). The ECM may very well be taking
away fuel because the A/F sensor is falsly reporting rich. Remember
low volts = rich on your B1S1 sensor.

thanks. I think I might have gotten the -23% backwards, I'm at work and
the car is at home (it's now the wife's car), I think it was 23% because
it also threw a P0170 Fuel Trim too Lean code the first time.

Like I said to Lawrence, the place I bought it from is going to look at
it tomorrow and have said they'll take care of it, but somehow I have a
feeling that means black tape over the CEL.

And the price for the 02 sensors at the dealer was about the same as
crappy tire, and they actually had them in stock unlike crappy tire.

Ray

 

[Ray]

It could be a bad connection ( corroded electrical connection ) to the
sensor, and not the sensor itself. Now we're supposed to diagnose
this sight unseen? I say, if there is _another_ one just like it in
the car, swap it with the known good one. See what happens. If the
problem switches from BANK ONE TO BANK TWO, or vice/versa. That would
be pretty good evidence.

Lg

relax.
I'm almost ready to consider 02 sensors a consumable item for cars
anyway, but my wife won't tolerate me throwing $600 in parts because of
a gut feel.
And unfortunately there's only two 02 sensors... one pre-cat, one post-cat.

If they don't fix it by the time I can have a "car day" then I'll be
crawling under the car to clean & test them.

So far, my first non-GM car since 1995 is not going so well.

Ray

 

[Ray]

Carl,
Indeed it seems that the part is not too expensive. I would guess that
the OP meant $300 installed. I checked and the standard flat rate
charge is 1.5 hours. That would put the dealer part and labor right
inline with $300. Many A/F ratio sensors are big$ but this one isn't
too bad. It's a zirconium oxide design with a lower current output and
range than the big boys I am used to seeing. This looks like an
excellent DIY job to save the OP some labor, unless the sensor is
frozen in the converter. That would be bad...

Toyota MDT in MO

<sigh>, no it's $300 CDN locally. I'm the labour.
I'm just not ready to start throwing parts at the car, but too stubborn
to pay a mechanic to fix it. Dammit, if I can swap cams in my race car
I should be able to diagnose this... but I feel like a blind man
describing an elephant. Maybe I shoulda bought a G6 or Malibu Maxx...
they're fwd and the 3.5 is 20 years obsolete, but at least I know how to
fix it.

Ray