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Old 07-06-2006, 04:50 PM   #1
Scooby Specialist
Member#: 3313
Join Date: Dec 2000
Chapter/Region: MWSOC
Location: Cincinnati
Default Front O2 sensor installation woes

Ok, so I finally got my replacement O2 sensor. It'd been dead for months, throwing a CEL and slightly hurting mileage. 01 2.5RS

I went to replace it last week. Even borrowed an O2 Socket. Get under the car, notice there is no way to access the sensor from the bottom, as the heat shield covers access to the actual nut from below. Can't approach at an angle, due to the headers. Reach around from up top...the socket can barely be put on, and no leverage. Try it with a big adjustable wrench and I can get on there, but again, it's pointed almost straight up, so no leverage. I sprayed PB Blaster several times. Nothing.

So I decided to try and pull off the heat shield. The various bolts(10mm, 11mm and 12mm) and various rear nuts(10mm and 12mm) on it are all rusted solid. Almost stripped them. Pull out propane torch and heat up all head bolts and get as much as I can on the rear nuts. Try again, nothing. Spray with PB, re heat, spray again, re heat, nothing.

So today, I try to drop the exhaust. The hanger bolt behind the cat? Won't come off. Went through all the options above...nothing.

I even tried torching the actual O2 sensor(on the nut) and reapplying PB Blaster again...tried reaching around with the adjustable wrench...no go.

Any other suggestions? I was going to cut the heat shield off, but feel like I'd go through a few cutting wheels on a dremel, as there's 5 bolts that I'd have to cut around. Don't feel comfortable using a sawzall in such tight spaces(car's up on jack stands, but still not that high).

I'd really not pay someone to do this...as every write-up on this indicates it's easy...but it's not. The even O2 Sockets will barely even stay on the sensor, with the end of hte socket hitting right where the cable comes out, so it's hard to keep it fully engaged.
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Old 07-06-2006, 05:38 PM   #2
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Member#: 5050
Join Date: Mar 2001
Chapter/Region: MAIC

the easiest way would be to drop the cat section or header or whatever and use an impact gun to spin the o2 sensor off. If you dont have one take it to any tire shop they will do it for 5$.

Or drop the assembly and use a 2.5ft breaker bar to crank that bad boy off. Remember to install the new one with a dab of high temp antisieze
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Old 07-06-2006, 06:37 PM   #3
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Join Date: Dec 2000
Chapter/Region: MWSOC
Location: Cincinnati

Well, since I can't get the hanger bolt off the cat...I can't drop any portion of the exhaust that will help.

I guess I'll keep trying to get the sensor off as is. I just hate paying someone $80 to do this.
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Old 07-06-2006, 07:33 PM   #4
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Join Date: Mar 2002
Chapter/Region: NWIC
Location: Beaverton, OR
2008 2008 Audi RS 4
2014 Audi S Q5


If you unlplug it and the use a box wrench you can access it. It is what, a 22mm? Probably something you'll have to buy but you can access it with that tool...

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Old 07-07-2006, 01:11 PM   #5
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Chapter/Region: NESIC
Location: NoVerm Brah......
2012 Speed3
Red Mica


I was able to get mine out in my old 92 legacy going at it from the top with a 22 mm wrench. I know the set up is a little different but it might work if you use a regular wrench instead of an adjustable. It was a PITA but i got it. I know you already tried going through the top though. I would say try going from the top again.
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Old 07-07-2006, 05:30 PM   #6
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Join Date: Sep 2004
Chapter/Region: BAIC
Location: SFBay
2000 Impreza 2.5RS


Seconding the drop the headers/cat tip: I know you said it was a bitch, but if you can find a way to drop it, you will save youself a ton of headache. The hanger for the cat section has a curved lip so the whole thing won't fall on your head when you unbolt it from hangers and midpipe. I mention this as if that hanger bolt is rusted into an amorphous blob, you could cut off the bolt head. Bolting it back up to the hanger obvoiusly won't work, but it will hold it in place well enough to attach it to the midpipe. At that point, it prob won't move around too much even without that hanger attachment.

This also allows you to put your wrench of choice on that O2 sensor easily, and dip/bang the end of that sensor in PB blaster and geasy engine and ruining it. They don't like chemicals on them..........
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Old 07-07-2006, 05:56 PM   #7
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Join Date: Jun 2005

Run the piss out of your car and get the catalytic converters super hot. This acts just like torching the bolts and will help in breaking the O2 sensor loose. Then from the top, put a 22mm or 7/8" wrench down in there and give it a good jerk. It should just pop loose. But be very careful with the hot exhaust!
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