2004 Legacy Outback Wagon H4 engine replacing upstream O2 sensor?

[hsholmes6]

Struggling to change out the upstream air / fuel ratio sensor (O2 sensor) on a 2004 Legacy Outback Wagon with H4 motor. Access to the sensor apparently is not available even when using a 22mm special sensor socket or any combination of socket knuckles or open-end wrenches. We've tried removing exhaust shield and converter shield but no joy.

The only way to remove / replace the sensor *seems* to be to remove the passenger front CV axle first. Any help would be hugely appreciated as we're stymied and stuck :-(.

Thanks in advance !!

 

[Ecmbuster]

With the new O2 sensor on hand, measure the hex and it should be 22mm.
If not, measure it to search for the best fitting tool.
Example images should help:
O2 sensor kit
Thread chasers
Crows foot wrench (6 or 12 point)
Tool extensions & handles

Never mind the propaganda that generally is included in the video.
It's a quick way of offering solutions if it fits.

Caution:
In the work that I do and with "O2 Sensor" tools, this has happened many times.
If for any reason the O2 sensor is difficult to rotate, then a shop torch is lightly applied to the"bung" of the pipe. Once loose and rotating, remove the defective unit.
Within the "O2 Sensor" tool kit, is a thread chaser to "clean and cut" the original threads.
This will save the replacement from being destroyed.
If the 22mm edges are rounded, then the shaft needs to be removed and apply a "brute force" gripping tool to have the sensor extracted. Again, chase the thread or the "bung" will be damaged.
With customer replacements, a small amount of "copper" anti-seize goes a long way.

Using any type of torch MUST be regarded as dangerous and the key word is "gentle".

The images are examples to help identify tools.