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Old 08-27-2001, 01:35 AM   #1
the Dabbler
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Default Screwed up my front O2 sensor

My front O2 sensor was completely, utterly, frozen in the stock pipe. After finally breaking it loose, it appears the threads are shot. Cross-threaded going in at the factory? Does that sound possible/likely? Could I have screwed it up somehow taking it out? Did anyone else have such a hard time?

Anyways, on top of the threads being mushed, the sensor makes a tinkling sound when shaken. I don't know much about O2 sensor construction -- is there a filament in there that can be broken? I was under the impression that they were fairly robust, mechanically.

At this point, I'm afraid to put it into my downpipe. First, because the threads don't look so hot, and I'm afraid of screwing up my relatively irreplacable downpipe. Also, I would hate to assemble the whole thing, then find that the sensor is actually busted.

So my question is, does anyone know the part number for the front O2 sensor assembly? I think I've found it on subaruparts.com ($75! -- expensive mistake), but I was hoping for some confirmation before I ordered it.

Any other comments welcome as well. But try not to flame -- I'm feeling bad enough already.

Thanks (MY00 2.5RS).
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Last edited by the Dabbler; 08-27-2001 at 02:11 PM.
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Old 08-27-2001, 08:02 AM   #2
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My rear one came out my cat. pipe the same way. I ended up buying a new one from the dealership. Sucks, but what else ya gonna do? :-/
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Old 08-27-2001, 10:36 AM   #3
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Use anti-seize on the new one so that the same thing doesn't happen again.

Ken M
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Old 08-27-2001, 10:48 AM   #4
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According to this page, http://www.northursalia.com/p...tsimpreza.html, the P/N for a front O2 sensor for the 99-01 RS is 22791AA00A.

I do not doubt that Subaru could have cross-threaded the sensor at the factory, but, just for the record, Subaru recommends that Subaru CRC (P/N 004301003) or its equivalent be applied to the threaded portion of the oxygen sensor and allowed to work for at least one minute before attempting to remove an oxygen sensor. That CRC stuff sounds like some kind of penetrating oil, like Liquid Wrench. Subaru also warns that the exhaust pipe will be damaged unless you wait for it to cool before removing the sensor. Bosch, whom I believe makes that sensor, also recommends using a special tool for removing hard-to-get-at oxygen sensors, either OTC 7189 Oxygen Sensor Wrench or Snap-On 56150 Oxygen Sensor Wrench (Crowfoot type).

Prior to installing an oxygen sensor, Subaru recommends that an anti-seize compound, SS-30 by Jet Lube, be applied to the sensor's threads, with special care taken to avoid getting any compound on the sensor's protector. The sensor should be torqued to about 21 Nm (15.2 ft-lb).
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Old 08-27-2001, 11:07 AM   #5
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Same thing happened to me a week ago when we took the o2 sensor out of Fitz's car to put on mine. I sprayed the hell out of it with Liquid Wrench, let it sit for a few minutes, and it still came out all messed up. It wasn't rusted in there, it was cross threaded. How much does a new sensor cost anyways?
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Old 08-27-2001, 01:27 PM   #6
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Glad to hear I'm not the only one who had problems.


8:

Oddly, my rear sensor came out with no fuss. Well, it wasn't easy, but no rounded corners or anything. I guess since it had just been changed with the O2 sensor recall (they changed the rear, right?), it hadn't had time to weld itself in there. And maybe the tech used some anti-seize.


Jon [in CT]:

So NOW you tell me. j/k

Actually, I didn't have any Subaru-spec CRC (whatever that is), but I did soak the thing in Liquid Wrench repeatedly. And I did see the "don't let it cool down" warning in the service manual, but since it took so long to get the thing off, it was pretty cold by then. Guess I could've heated it up with a lighter or something. What is the mechanism by which it gets damaged if cold? Are the threads on these things designed to mate better when the metal is expanded a little? Maybe that's why it looked cross-threaded coming out. At any rate, the pipe looks okay. The sensor is toast, though. So what does an Oxygen Sensor Wrench look like? Is it like a flare nut wrench? I was thinking of going out to get one (flare nut wrench) when it finally broke loose.

I am DEFINITELY putting anti-seize on this thing when it goes back in...


RyanC:

Subaruparts.com is selling an "Oxygen Sensor - Front, 6/95 and newer" for $75.96 (!). The part number that Jon [in CT] gave (from Ravensblade) appears to be another part ("F Oxygen A/f Sensor"), for $63.19. Not sure which is the right one, although Ravensblade seems to be more specific, so I'm inclined to go with that.

Anyone bought one of these that would care to confirm the p/n?
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Old 08-27-2001, 05:09 PM   #7
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the Dabbler wrote: "And I did see the "don't let it cool down" warning in the service manual, but since it took so long to get the thing off, it was pretty cold by then. Guess I could've heated it up with a lighter or something. What is the mechanism by which it gets damaged if cold? Are the threads on these things designed to mate better when the metal is expanded a little?"

NOOOO

I meant the opposite. Here's the warning in Subaru's own words:

CAUTION
When removing the oxygen (A/F) sensor, wait until exhaust pipe cools, otherwise it will damage exhaust pipe.


I don't want to get into a hot/cold expansion/contraction discussion. My theory is that the exhaust pipe's threads tend to soften when the pipe is hot. Hence the warning.
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Old 08-27-2001, 06:23 PM   #8
the Dabbler
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Quote:
NOOOO

I meant the opposite. Here's the warning in Subaru's own words:

CAUTION
When removing the oxygen (A/F) sensor, wait until exhaust pipe cools, otherwise it will damage exhaust pipe.
That's bizzare! I have the service manual, and I could've sworn I read it the other way last night! I thought that was strange at the time, but I figured, what the hell do I know?

Well, anyways. The O2 sensor is screwed up.

Anybody got that part number?
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Old 08-28-2001, 01:08 AM   #9
the Dabbler
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Jon [in CT]:

Check this out. This is weird...

Quote:
NOOOO

I meant the opposite. Here's the warning in Subaru's own words:

CAUTION
When removing the oxygen (A/F) sensor, wait until exhaust pipe cools, otherwise it will damage exhaust pipe.
Okay, I went back and read my factory service manual, and this is what it says (vol 4, Secn 2-7, p. 38):

"CAUTION:
When removing front oxygen (A/F) sensor, do not force front oxygen (A/F) sensor especially when exhaust pipe is cold, otherwise it will damage exhaust pipe."


This seems to be the exact opposite of your quote!

Maybe they're saying that no matter what, you'll damage the sensor!

btw, which year service manual were you quoting from (mine is an MY00)? Maybe one of them has a typo, if you could call it that.

Last edited by the Dabbler; 08-28-2001 at 01:15 AM.
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Old 08-28-2001, 02:06 AM   #10
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If it's cross threaded temp won't matter. Has anybody checked out aftermarket O2S??? Maybe cheaper and better quality, like a Bosch or something.
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Old 08-28-2001, 12:48 PM   #11
the Dabbler
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Actually, it is a Bosch.

And it looked cross-threaded to me. As I stated earlier, I just wanted to understand the mechanism by which Subaru thinks it will be damaged if removed hot... or cold... or whichever, depending one which service manual you believe. I thought perhaps this mechanism, whatever it is, could result in something that looked like a cross-threaded part.
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