O2 Sensor in 5 Hours?

[truckster]

So, here's how I spent a significant chunk of my New Year's Day: My daughter has a 2005 Subaru Outback. Her emission test is due in January and she had a check engine light on. I scanned it and came up with P0420 - bank 1 sensor 2 catalyst below efficiency threshold. No problem, right?

Well, to start off with, this is a California emissions car, so there are 3 catalytic converters and 5 O2 sensors. It should be the one behind the first cat on the right (passenger side) bank, so I get the right sensor, put it up on ramps, and go to work, thinking 30 minutes at most and maybe as quick as 15.

First, the connector is right up against the wiring harness. It takes me more than 15 minutes just to get it in a position where I can release it. So far, not so good.

Then I get under the car with my O2 sensor socket and 3/8 drive ratchet. The O2 sensor isn't budging. After a liberal application of Liquid Wrench, I put a cheater on the wrench and try again. No luck. I get out my torch and give it a nice blast of heat and try again. No luck. I mean, it's not even budging a hair. I keep going between the penetrating oil and the heat, making my garage and me smell divine, until the wrench finally moves. Nope, it's not loosening; the hex on the sensor rounded off.

Now the exhaust manifold and pipe have to come off. Because it's a CARB emissions car, the two pipes come into a Y just ahead of the third converter. There's barely room to get a wrench in there, but it doesn't matter, because road debris has damaged the nut to where a wrench won't hold it. So I get out the angle grinder. One of the two bolts falls quickly. The other one is tucked tightly in the Y, so I get out the Sawzall. Nope, can't get in there. I get out the Dremel and manage to cut about 2/3 of the way through, but there's not enough room to continue. So I have to get out the plasma cutter, and I somehow manage to get the plasma stream in the right place and remove the pipe. I really need a lift...

So now I just have to get the O2 sensor out. My first attempt is to hammer a socket onto the sensor and hit it with my impact wrench. It starts spinning and the end of the wire spins around and hits me in the arm and in the thigh. Ouch; I should have cut that off first. No matter, because now the hex is really rounded. So I take the angle grinder and cut large flats on opposite sides. I get an open-ended wrench on there, but it's not moving. Next up, a pair of very aggressive vise grips with V-shaped jaws and a long cheater pipe. I give it more heat and more juice, but it's just removing more material...

Now things are getting desperate. I decide to cut away everything above the base of the sensor. Did you know that the core of an O2 sensor is made of zirconium dioxide, which is only slightly less hard than diamond? I finally cut through it with my angle grinder after going through a couple of cutoff wheels and sending bits and pieces of grinding wheel and zirconia all over. I then take a 3/4 inch nut and weld it on my highest heat setting, making the thing glow bright red, almost white. Now I've got something to put my impact on, and the remnants of the O2 sensor finally come out.

Now I get to go to the auto parts store, because I need some exhaust gaskets that I hadn't planned on replacing. Most of the reassembly goes well, but I discover some broken grounds that I repair while I'm under there. Finally I clear the codes and hope not to see the underside of that car for a good, long while. By the way, did you know that all Subarus leak oil from almost every conceivable seal and gasket?

So that's how I spent my New Year's Day afternoon. How was your day?