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Discussion Starter · #1 ·
I thought they had a nut that you put a wrench on, but mine is just round??
(96 mini, rear o2)
 

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Just take the nuts off...

MLB said:
I thought they had a nut that you put a wrench on, but mine is just round??
(96 mini, rear o2)
Look down there again. On either side of where you tried to put your wrench is a nut on a stud. The O2 sensor is flanged...
 

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It is a regular 6 sided nut. Over time they will oxidize and can make it tough to get off.

If and when you get it off, find a good hardware store that has high quality stainless fasteners and get a high grade stainless nut to put back on it.

I live right off of the Cheapeake Bay and everyone by my had a boat around here. There is a very nice hardware store about 10 minutes from my shop and they carry all kinds of stainless hardware. When I take something off of my truck, I usually replace the nuts and bolts with stainless.
 

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Discussion Starter · #4 ·
Ok, I've just looked at the replacement URD sent me. So you're saying there is a nut on the existing o2 that I'll take off and reuse to hold this one?
Thanks again
Big blizzard here and very cold, so i haven't felt like crawling around underneath :)
 

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Using brass nuts on exhaust stuff if usually best, but thats usually on conecting flanges like header to downpipe, not stuff like an o2 sensor or is it? Will brass corrode bad just like steel? I dont have the corrosion problem here in oregon as bad as some of you other people say you have it so I dont really know.
 

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There should be two nuts...

MLB said:
Ok, I've just looked at the replacement URD sent me. So you're saying there is a nut on the existing o2 that I'll take off and reuse to hold this one?
Thanks again
Big blizzard here and very cold, so i haven't felt like crawling around underneath :)
I'm not sure what you are looking at. Doesn't your sensor look like this?

See the two holes on the flange? There should be a stud with a nut through each of those holes. Remove the old nuts and pull off the old sensor. Install the new sensor. New nuts are a good idea if you are in the rust belt.
 

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when cleaning your 02 sensors, should u clean both of them? Or is there only 1?
 

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CYi5 said:
when cleaning your 02 sensors, should u clean both of them? Or is there only 1?
There are 2, one upstream and one downstream of the cat(s). The upstream one provides feedback to the ecu for fuel trim. Downstream just monitors the catalyst I think.
 

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flatlandtacoma said:
There are 2, one upstream and one downstream of the cat(s). The upstream one provides feedback to the ecu for fuel trim. Downstream just monitors the catalyst I think.
That is how I understand it as well, and if there isn't any check engine light the second one doesnt need cleaning. It normally gets cleaner exhaust after it has gone through the cats anyway. The first one would need the cleaning to get more accurate readings and adjust your fuel trim accordingly.
 

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Clean them both, the downstream one will probably not be too dirty though
 

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Discussion Starter · #11 ·
The code I have is for the rear sensor. My gas mileage is down 3-4 mpg since the CEL came on. It's got SOMETHING to do with the EFI.
 

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MLB said:
The code I have is for the rear sensor. My gas mileage is down 3-4 mpg since the CEL came on. It's got SOMETHING to do with the EFI.

Well in that case, it may be something else. You should get the exact code then come back and post it so someone can look it up and people could post what is the common cause of it. Most of the time the codes for the second O2 means your cats may have gone bad and this can cause the lower mpg, but the only way to get closer to the problem is by posting up the exact code you read.
 

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They are not what one would normally clean but simply replace. However, you could make sure that the air openings on the outside of the sensor are open but you do not need to remove the sensor for that. You may be able to burn some contaminants off the sensor tip with a propane torch or something but you don't clean them with solvent or anything like that.

If you do R&R, be sure to put some antiseize on the mounting studs.
 
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