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How to install new rear O2 sensor if O2 is welded in place?

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My 2002 H6 OBW daily driver. The rear O2 sensor is welded to the bung, nice size bead. I tried removing it but no budging.

 

Cut/grind the weld off?

 

If I cut midway through the bead or a bit lower I'll have to cut below the hex part on the O2 sensor and then can't remove the sensor (easily).

 

And the threads will probably be mangled and unusable...except that's the same threads as a spark plug so I can use a spark plug thread chaser to clean those up. That's probably the best option.

 

I could add another bung somewhere maybe. That sounds difficult unless I just have an exhaust shop do it. They might not even weld into the catalytic converter though?

Edited by grossgary

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Yeah I vote new bung too, but I'd probably cut the old one off (quick with an angle grinder/cut-off wheel) flush with the pipe and weld the new one on top. Bungs are only a few bucks and I'm sure your old threads are gonna be trashed.

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Yeah I vote new bung too, but I'd probably cut the old one off (quick with an angle grinder/cut-off wheel) flush with the pipe and weld the new one on top. Bungs are only a few bucks and I'm sure your old threads are gonna be trashed.
that's probably the way to go not much space on this tiny area it's on anyway and get the old one outta there.

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My 2002 H6 OBW daily driver. The rear O2 sensor is welded to the bung, nice size bead. I tried removing it but no budging.

 

Cut/grind the weld off?

 

If I cut midway through the bead or a bit lower I'll have to cut below the hex part on the O2 sensor and then can't remove the sensor (easily).

 

And the threads will probably be mangled and unusable...except that's the same threads as a spark plug so I can use a spark plug thread chaser to clean those up. That's probably the best option.

 

I could add another bung somewhere maybe. That sounds difficult unless I just have an exhaust shop do it. They might not even weld into the catalytic converter though?

Boy, anyone else and I'd have asked if you were really looking at the O2 sensor or the bung being welded to the cat!

Is this how you got the car?

How many miles? Did someone simply over-wrench a rusted old O2 sensor out last time?

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Boy, anyone else and I'd have asked if you were really looking at the O2 sensor or the bung being welded to the cat
LOL, that's how i felt posting this.

 

Is this how you got the car?

How many miles?

yes, have never looked at the rear O2 sensor until now, at 202,000 miles, got the car at 130k. no one else works on my cars, i don't even take them in for new tires. it looks very much like it's welded in place.

 

I bought the vehicle salvage (wrecked) and repaired it. Front exhaust had some welding already done to it when I got it - so it's not too surprising maybe they also did something with the rear O2.

 

I would like to find the stock rear O2 sensor location and picture if i could. Haven't gotten anything from google images yet.

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My guess would be someone replaced the rear sensor and stripped the threads out of the bung. Probably cross threaded the new sensor or the threads pulled got chewed out by the old one. What better way to fix it than with a welder right?

I would just cut the whole deal off and weld on a new bung. A competent exhaust shop should be able to do this for no more than a half hour or so labor, plus a few $ for the new bung, which they should also have.

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My guess would be someone replaced the rear sensor and stripped the threads out of the bung. Probably cross threaded the new sensor or the threads pulled got chewed out by the old one. What better way to fix it than with a welder right?
since the front two exhaust runners from the head ports are both cut and have new straight pipe welded in for a few inches it's obvious this thing saw some work and your guess seems likely.

 

 

From Opposed Forces

 

O.

thanks O.! i looked at that pic and the O2 sensor was just off to the side and avoided my notice. when you posted it i figured i must have missed it, thanks. that's about where mine is. i thought it was more central on the converter that looks more to the side but probably same.

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Only other alternative is like my 04 BE. It was a Ca. emissions (PZEV state here).

Although it was an H4 it borrowed the headers and exhaust from the H6.

It had a total of 5 O2 sensors!

In attached pic you can see the 2nd sensor just behind the cat, in front of tranny support crossmember.

 

O.

post-19929-136027661801_thumb.jpg

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Only other alternative is like my 04 BE. It was a Ca. emissions (PZEV state here).

Although it was an H4 it borrowed the headers and exhaust from the H6.

It had a total of 5 O2 sensors!

Looks like there are:

5 O2 Sensors on 04-05 H6's

3 O2 sensors on 01-03 H6's

 

link showing the difference from an online Subaru dealer:

 

http://www.subaruoutback.org/forums/66-problems-maintenance/36330-2003-outback-wagon-h6-3-0-o2-sensor-location.html

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