How to replace a Oxygen Sensor

The other day I took my 4.0 YJ in to for an emissions check and was surprised to learn it failed. The engine only has about 60k miles on it and I take good care of it, yet the carbon monoxide levels it was spitting out were 3 times (!) higher than the maximum. Then I noticed that somehow the wires going to my oxygen sensor on the exhaust pipe had been severed right where they connect to the sensor and there was no way to splice them. Oh well, 60k miles isn't a bad mileage to replace an oxygen sensor and this may be what's causing my emission problems (I still don't know for sure as of this writing). Turns out replacing these puppies is easy.

Go to your favorite auto parts store (I bought mine at Checker/Kragen for ab out $50) and buy a Bosch O.E. Type, part number 15704. It comes with the wiring permanently attached. Now this is the part number for my 4.0 but it may very well be different for the 2.5, the never 4.0 and the 4.2, so check with the auto parts people at the store. Also, get an oxygen sensor socket. I have tons of tools but nothing worked like this socket. Checker sold this socket for $14 but Auto Zone loaned a really neat kit to me for free, with a $15 refundable deposit. Do it, trust me.

Now for removing the old one. You'll find this from under your Jeep next to your oil pan on the drivers side very close to where the two sections of exhaust pipe are bolted together. Oh, and it's actually on the exhaust pipe. My Jeep is 9 years old and the old one felt like it was welded on. I was very concerned about breaking it off or even cracking the manifold or bending the exhaust pipe. I'm not sure whether or not there is a danger in doing this, but I sprayed some lubricant (WD-40 type) around the base of the old sensor and left it for an hour or so. I then attached the special socket and muscled it. It eventually broke lose and loosened by hand. Once you get it out, detach the wiring connector (follow the wires up till you see it) but save the little white thingy that attaches the connector to the bracket on the engine. You'll need to re-use that and it's simple to get off. Yeah I know, mine wasn't in great shape either but it still works. Next screw in the new one. Tighten but not too tight (I never found a torque spec). Connect the wires and you're set!

I hear it takes a good 100 miles of driving for your rig to properly adjust to the new part.

The Bosch Sensor (looks almost exactly like this)

Where everything is located

The wiring connector