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Old 11-06-2012, 05:12 PM   #1
ChrisTahoe
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Default 04 STi P0171

So I've got this code, and the shop confirmed my suspicion of a bad O2 sensor. However, the shop said it was my aftermarket header that caused the sensor to fail (because the header runs hotter), and that a new sensor would also fail soon.

I've never heard of headers causing an O2 sensor to fail, but that doesn't mean he isn't right, I was just wondering if someone else could confirm or dispute these claims.
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Old 11-06-2012, 05:22 PM   #2
STIBungy
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Only instance I've seen of an aftermarket header destroying an O2 sensor is a new one that had oil used in the bending of the tubing ruin it. Told the guy to run some brake parts cleaner, replace the O2 sensor and all was good afterwards.
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Old 11-06-2012, 05:39 PM   #3
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OK.....

What aftermarket header do you have?

How was the sensor ruined? Heat? Burned through wires?

I have never even seen a header destroying an o2 sensor. Just human error.
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Old 11-06-2012, 05:52 PM   #4
ChrisTahoe
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It's an Agency header.

O2 sensor was just fouled. No burnt wires or anything.

Been 8k+ miles on my current tune from Cobb SoCal.
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Old 11-06-2012, 06:30 PM   #5
DHRDAN
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I'm on my 3rd O2 sensor.... i say they last like 1.5yrs..... though i think the reason mine fail is because i have no tune.


My rear also died very quickly since i put my 3" straight pipe exhaust.


Just throw a new one on... but make sure your tuned.


Edit: i'm also running an 04 STI engine.
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Old 11-06-2012, 07:35 PM   #6
ChrisTahoe
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We'll see what happens. Only reason I'm not changing it myself is lack of tools.

I think the mechanic might be not the most knowledgeable, especially after he said the AP can't show live data, and only reads averages.

He also said that the car was running lean. Isn't it actually running rich? The broken O2 would cause the ECU to believe there is a lean condition, when there isn't, and then dump more fuel, thus running rich? Do I have that right, or am I missing something that makes the mechanic's statement correct?
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Old 11-07-2012, 10:49 AM   #7
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How did they confirm a 171 was a bad o2 sensor? It usually is not.

Subaru front o2 sensors dont seem to last forever, but they dont wear faster in a tubular manifold that is silly.

If you got a 171 code you should use your AP to look at your AF Learning values in the A-D range. Im more willing to bet you have a boost or other post maf leak.
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Old 11-07-2012, 11:04 AM   #8
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Quote:
Originally Posted by Wicked Innovation
How did they confirm a 171 was a bad o2 sensor? It usually is not.

Subaru front o2 sensors dont seem to last forever, but they dont wear faster in a tubular manifold that is silly.

If you got a 171 code you should use your AP to look at your AF Learning values in the A-D range. Im more willing to bet you have a boost or other post maf leak.
I will take a look at it. My boost values are fine as well as my idle, so I assumed there weren't any leaks.
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Old 11-07-2012, 11:14 AM   #9
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In order to get a 171 code from the o2 sensor, it would have to be operational, but skewed lean all the time. Ive never seen this happen. Its worth taking a look before replacing a $200 sensor that may still be fine.
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Old 11-07-2012, 11:21 AM   #10
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Quote:
Originally Posted by Wicked Innovation
In order to get a 171 code from the o2 sensor, it would have to be operational, but skewed lean all the time. Ive never seen this happen. Its worth taking a look before replacing a $200 sensor that may still be fine.
While monitoring the O2 sensor values, it's stuck at 1.8v and doesn't seem to move from there. If there was a leak, would my AF value be so lean that it'd stay at that constant voltage/AF reading?
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Old 11-07-2012, 12:29 PM   #11
Wicked Innovation
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if the ecu thought the o2 sensor was bad, there are a bunch of front o2 codes it can throw.

it could be yes
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Old 11-07-2012, 12:41 PM   #12
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My symptoms are consistent with #8 on this link:

http://forums.nasioc.com/forums/showthread.php?t=475620

And the 171 code is known to be thrown from a bad front O2 sensor as other Subaru owners have experienced the same issue.

I'm pretty confident it's the sensor, I had just never heard of a header causing O2 sensors to foul.
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Old 11-07-2012, 01:58 PM   #13
Wicked Innovation
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If that is your problem, Ill chalk it up as the second time Ive seen it. Normally I would expect to see one of the front o2 codes to trip as well.

Report back Im interested to see if this is the resolution.
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Old 11-08-2012, 04:27 PM   #14
ChrisTahoe
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Update: O2 sensor was replaced. I did some in town cruising and some highway driving. All is good. CEL didn't come back and when I try and read sensor data on my AP I get real values (it's not stuck on 21).
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Old 11-08-2012, 04:28 PM   #15
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awesome! congrats on fixing it
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