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Discussion Starter #1
Had the check engine light come on on my way back from skiing yesterday, and just now finally got to check it. The scanner comes up with P0130, 'Front Oxygen Sensor Circuit Malfunction"

I also finally found where I have an exhaust leak - the weld of the last pipe onto what looks like a small resonator ( right under the rear seats) is broken. Pipe is still well in place, but with the leak there, i would expect a change (decrease) in exhaust back pressure.

The code reader (an Innova 3160g) says check the following;

1 - Check harness between the ECM and sensor
2 - Check exhaust system (yup, broken as described above)
3 - A/FS is contaminated, damaged, or has failed ( I assume A/FS means Air/Fuel sensor?)

A couple questions:

In this case, with the exhaust broken an leaking as described, would you expect that to be the cause of the code?

In any case, even assuming a sensor failure, what damage could be done if I drive the 250 miles (round trip) to the ski area again tomorrow? The chances of me fixing anything tonight are slim to none, partially from the time available, and partially because there is melting snow that would make the job rather miserable!

Advice?
 

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I dont think you are going to kill an O2 sensor that quickly unless you are dumping unburned fuel into the exhaust & you'd have a cat thats glowing cherry red it that were the case. Im guessing the exhaust leak is the culprit. Fix the leak & the code will probably not return.
 

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I had that code a while back, needed a new front o2 sensor to replace the original. as I continued to drive the car it would get progressively worse over weeks. I could still drive it, however on grades = minor misfires/ bucking.

I made the following thread really as a exercise in using rom-raider. apparently later cars make slightly different codes in the 013x sequence.

http://www.subaruoutback.org/forums...89-p0130-2002-ej251-climbing-grades-fast.html
 

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Discussion Starter #4
Well, I'll keep my fingers crossed and go skiing tomorrow!

And will order new sensors right now. Subaru only?

And only those specified for 2000-2004 OB 2.5 autos?
 

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Well, I'll keep my fingers crossed and go skiing tomorrow!

And will order new sensors right now. Subaru only?

my H4 car has Densos in them, I would also consider NGK=NTK . I have bought such things from RockAuto and Amazon.
(local parts store chains like to overcharge on such things it seems).
 

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In this case, with the exhaust broken an leaking as described, would you expect that to be the cause of the code?

Advice?
An exhaust leak that far down the pipe will have almost zero effect on the front O2 sensor.
You would require a leak either at the manifold, or between the front and rear O2 sensors.

A/FS is contaminated, damaged, or has failed I assume A/FS means Air/Fuel sensor?
Correct, A/FS refers to the oxygen sensor, although one could mistake it to mean an air flow sensor; a component commonly found in the intake duct, between the air filter and the throttle body.
 

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And only those specified for 2000-2004 OB 2.5 autos?
I pick part #s with rock auto, then amazon, then double check with the manufactures website. and make sure they are all the same.

and concur with Gen2lover. exhaust leaks that far back just make for some noise, and maybe some faster rust.
both my subarus have of the factory flanges cut off and a cheapo union welded in on these areas of the exhaust pipes.
(no big deal for any shop with a pipe bender,) so get it fixed while you still have good stuff there to weld to.
 

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Discussion Starter #8
Hmmm... Thought I'd read a few post saying Sub only for these.
 

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I think Denso was the OEM supplier, but I won't swear to that.
 

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Discussion Starter #10
The Denso and Delphi prices on Rock Auto are about 1/3rd of anywhere else i see so far.
 

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Discussion Starter #11
The Subaru parts site shows only one front sensor. Is that correct?
 

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Discussion Starter #13
Any idea what the wrench size is for the Denso sensors? may as well get the special wrench while I'm at it - or is it not worth it?
 

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Discussion Starter #14
Well, after a quick crawl underneath, it is the weld from the second resonator to the rear pipe that rusted away. At least the rear pipe extends some distance into the resonator, so it looks like at least I don't have to worry about them separating during the trip. Will have to finally take a good look at the whole system on Saturday after the sensors come in Friday to see what I may as well replace now so that i don't have to worry about it later.

Also found a big upwards dent in the floor under the rear left passengers seat. Nothing broken, thankfully - just dented. Will have to look at it later sometime to see if it is worth knocking back into place.

Oh, the fun stuff you find on an e-bay car! :)

Oh yes - the check light came on during the trip back, after which it seemed like the fuel gauge started dropping a LOT faster, which makes sense. Still managed 25 mpg cruising at mostly 75 for the duration, so it makes me hopeful that it will jump up to 30 or so once the sensor is replaced ( replacing both).
 

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Discussion Starter #15
interesting - the check engine light shut itself off this morning just a couple miles into the trip. No real change in gas mileage, though.

New Denso sensors arriving tomorrow - a job for Sunday, since the Hanenkamm downhill race is on the tube Saturday afternoon! :)
 

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interesting - the check engine light shut itself off this morning just a couple miles into the trip. No real change in gas mileage, though.

New Denso sensors arriving tomorrow - a job for Sunday, since the Hanenkamm downhill race is on the tube Saturday afternoon! :)
front one is causing the trouble.

back one just makes the p0420 code. (such may get changed more often,)

removing such from old cars: penetrating oil, and a little heat, but not enough to deform the threads. getting a wrench on the old one may require cutting the old one in half with a sawzall. (on a a old subaru with some rust: the longer they were in the harder they are to get out).
 

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Discussion Starter #17
Will most likely only do a quicky patch-job on the pipe this Sunday, replace the sensors, and give the whole exhaust system a check-over to see how everything else looks before deciding on the next step.

Looked at Rockauto for what they have for replacements, but they list complete systems only for EJ253 engines, but do have that one pipe available for my car.

Question: Would the only real difference between an EJ251 and the EJ253 system be in the very front header pipes? I unfortunately no longer have my tube bender, so making up a stainless system in-house is no longer a possibility (nor really something that I would feel like undertaking any more even if i did still have it! :) ).
 
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