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1999 L
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21 Posts
Discussion Starter · #1 ·
I need to replace upstream O2 sensor on my Subaru Forester L 1999. Do I need to remove the shield under the catalitic converter or it's possible to unscrew the sersor with some kind of "socket" wrench ? All the bolts which hold the shield are very rusty and I'm not sure if it's possible to unscrew them. So far I have managed to unscrew 1 and destroy 1 bolt.
 

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The Modfather
2019 Impreza 5dr Sport - Manual
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8,071 Posts
First off welcome to the forum, if you look here:

http://www.scoobymods.com/oxygen_sensor_removal_02-t5464.html?t=5464

I have info with pics, there is a pic of the 99 system and it will show you where it is. It's a shot of my 99 Impreza RS but it will be similar. You should not need to remove the heat shield to do the front (or rear for that matter) but having the proper tool helps. Most automotive stores will lend them out when you leave a deposit.
 

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The Modfather
2019 Impreza 5dr Sport - Manual
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8,071 Posts
Happy to help :) Just a quick word about a replacement sensor. You can get a universal one (where you need to cut off the old harness plug from the sensor and attach to the new one) or one that will plug directly into the OEM harness w/o any splicing. Universal ones will work but I've read of spotty results and sometimes people have issues. I think it may be due to the splicing, the wire is stainless steel and they use a special plug contraption to do the splicing. If you haven't gotten one yet I'd encourage you to get one that you won't need to splice. Either an OEM one from Subaru or other place. Just to avoid any problems. They are more expensive though but IMHO worth it. If you look in the vendor section on this site you will find some vendors that supply OEM parts at a discount. Just a heads up. Good luck!
 

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The Modfather
2019 Impreza 5dr Sport - Manual
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8,071 Posts
good deal let us know how things turn out.

(where in NJ are you? I'm from there originally - Born in Jersey City but lived over the state at one time or another)
 

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1999 L
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21 Posts
Discussion Starter · #7 ·
Peaty,
Crows foot style tool worked perfectly.
I borrowed it in the nearest "Advance Auto Parts" and replaced the sensor in about 20 minutes. I didn't try to experiment with a simplier "slotted socket" tool because it's not allowed to repair the car at my appartment complex and I wanted to finish everything quickly.
P.S. I've been living in East Windsor (NJ) for 8 years since I came to US.
 

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2001 Forester Slushbox
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1,777 Posts
Peaty,
Crows foot style tool worked perfectly.
I borrowed it in the nearest "Advance Auto Parts" and replaced the sensor in about 20 minutes. I didn't try to experiment with a simplier "slotted socket" tool because it's not allowed to repair the car at my appartment complex and I wanted to finish everything quickly.
P.S. I've been living in East Windsor (NJ) for 8 years since I came to US.
Welcome aboard and where you from originally?

(this forums great ain't it,so much info)
 

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The Modfather
2019 Impreza 5dr Sport - Manual
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8,071 Posts
Glad you got it sorted out. I have both types of O2 removal tools. Depending on where and how the sensor is situated, one usually works better than the other.

I actually lived in East Windsor for a few years myself. I worked in Cranberry at General Foods back in the Early 80's then moved over to Heights Town for a little while.
 

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The Modfather
2019 Impreza 5dr Sport - Manual
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8,071 Posts
Do a search and if you come up empty just start a new one in the appropriate forum. I'm sure someone will help out :)
 

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2003 Forester
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20 Posts
Can't get it out - no leverage!

I also need to change the front Air Flow sensor on our 2003 Forester with the 2.5 NA. So I looked at the pics and great explanation by Peaty, and also got the crow's foot socket. But when I crawled under there and got the socket on the sensor, there was literally no room for the breaker bar to move to loosen it. One of the heat shield's "ears" that stick out for the bolt to go through is directly in the path of the socket movement (I will try to take some pics and post them). I tried every way I could fit my hands up in there, even tried the flair wrench that was suggested, but I cannot get it on the sensor at any angle that allows any movement.
I am at a loss for what to do next. Any suggestions will be greatly appreciated.
 

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1999 L
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21 Posts
Discussion Starter · #15 ·
I'm not sure if your car has the same design around upstream O2 sensor. Try to put "crows foot" on the sensor at different angles/rotations and rotate and move the breaker bar differently. The space is very limited, but there should be some combination of those positions/rotations that allow some limited movement to unscrew the sensor a little bit. After that you might be needed to repeat everything again.
 

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2007 Mitsubishi Pajero 5spd Automatic
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3,572 Posts
The thing is I have allready replaced this sensor on the heatshield with a front O2 sensor. So I begin to wonder if I replaced the sensor with a sensor not belonging there but that's weird since the it had the excact same plug and all. Only the tip of the sensor was a bit different. But besides that it all fits.
Could it be that my O2 sensor sits where it is on the pic and not further down on the other side?
If so then I replaced the correct sensor atleast :shrug:
 

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1999 L
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21 Posts
Discussion Starter · #17 ·
Elmy,
I'm not sure what could it be but I don't know any other sensors "after" the engine except O2. If it's "after" the engine and before the catalytic converter then I think it's upstream O2 sensor.
 

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2007 Mitsubishi Pajero 5spd Automatic
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Elmy,
I'm not sure what could it be but I don't know any other sensors "after" the engine except O2. If it's "after" the engine and before the catalytic converter then I think it's upstream O2 sensor.
You can just see it on the pic sticking up with the end and the wires sticking out. I'm thinking it is the upstream O2 sensor.
Replaced with sensor 22690-AA321
 

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Don, King of the parts diagram
MY11 WRX STi Sedan 6MT
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5,984 Posts
You can just see it on the pic sticking up with the end and the wires sticking out. I'm thinking it is the upstream O2 sensor.
Replaced with sensor 22690-AA321
Elmy,

That would be correct.

For pre ODBII (EODB) cars the first O2 sensor is in the top of the down pipe, although all of Subaru's parts illustrations use a standard layout and show it being in the manifold as for the later car.

On the exhaust diagram it is shown in its correct position but to obtain the part number you are referred to the manifold diagram.
 

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2007 Mitsubishi Pajero 5spd Automatic
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3,572 Posts
Elmy,

That would be correct.

For pre ODBII (EODB) cars the first O2 sensor is in the top of the down pipe, although all of Subaru's parts illustrations use a standard layout and show it being in the manifold as for the later car.

On the exhaust diagram it is shown in its correct position but to obtain the part number you are referred to the manifold diagram.
Thx man. Then I changed the right sensor :woohoo:
 
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