I found the front 02 sensor on my 03 Forester but can't get it loose.  I have tried both regular and offset sockets but the exhaust interferes.  Any suggestions would be most welcomed.

if you can reach it safely, try loosening it when it's hot from driving.

 

try heating it - even with a propane torch, then spray with a penetrant like Kroil, PB Blaster or even ATF:Acetone 50:50 ,wait, try again, repeat, etc..

 

be careful of fumes/fire.

Edited December 22, 201510 yr by 1 Lucky Texan

jack it up and remove the heat shield bolts (you'll probably have to cut them off).

This way you can raise the shield enough to get an open end onto the bung and another on the sensor itself.

If you don't a good 19mm open end, a small pipe wrench will work also.

Spray with PB  and try to tighten a bit to break the tension. Then unloosen.

 

O.

If you know you're replacing the sensor anyway, here's the process I used the last time I had one really stuck. The o2 sensor specific socket would flex and slip.

 

I dropped the exhaust from the heads and the trans exhaust support so it could flex down. Then from under the car I cut the o2 sensor off about an inch above with an angle grinder. Then I could slip a socket over the top (21mm? Cant remember exactly) and with a breaker bar it spun out just fine.

 

Heat and some PB blaster are a good combo as well.

The reality is that many jobs rated "piece of cake" are in actually tough in many cases due to dozens of potential problems that mechanics are well versed in but do it yourselfers are not.   If I want to work on anything on my car I have to do it outside on the pavement in a parking area that forbids working on cars, but not enforced.  If you have lots of tools that helps but technique is critical.  I wonder what the prevailing wisdom is on PB Blaster vs. WD40 vs. Liquid Wrench.

Ive used them all, WD40 is useful for many things, but as a penetrating oil it really doesn't work. 

 

PB is usually my Go-to since most of the stores around here carry it.

 

I use some stuff called Buster at work, but its only available by the case straight from ATCO, the manufacturer. A case would last a DIYer a lifetime if the aerosol didn't get out. I have been using about a can a month, so a case will probably last me 12-15 months. 

 

Anyway, Back on Topic...

 

O2 sensors are easier to remove hot, IF you can get access to it without burning yourself.