O.k. I'm replacing an O2 sensor (upstream) on an 04 Trailblazer. Well, the darn thing won't budge! It's not exactly in a good spot, plus I don't want to crank on it too hard with the nothched socket and break it off. Would it help to let the manifold warm up and then try it or would that only strip it out?

Use a torch to heat up the bung. Hotter than the normal exh temp.

What he said ^

plus, any "open side" socket or wrench will be weaker than a solid wall socket. The open types tend to give, and then you end up rounding off the sensor hex.

If you are replacing the sensor, you won't need the wire for it... so cut it off to allow use of regular deep well 7/8 socket (impact socket would be nice) or closed loop wrench. It will be much stronger.
Same trick works wonders for brake line fittings. Cut the line near the hex nut to be able to use a regular socket. Helluva difference. I do this for a living.

I would do the torch method, if I had one.

I know what you're saying about the weak side of the socket. Every time it gets a little crooked, I get nervous. I'm thinking about sacrificing a 7/8 deep well by cutting the end off and welding on a big nut, sort of like a spark plug socket. That way I can slide the wire harness and all through it.

Like I said.. if you are replacing the sensor, cut the wire off right at the sensor. Then there is no need for a special tool.
You don't need the wire since you are throwing it away.

It's not in good spot and I'm worried about breaking it off. I've broken enough exhaust manifold bolts and stubborn spark plugs over the years, so I'm a little gun shy. I'm hesitant to cut the wires off for fear I really won't be able to get it out. Anyway thanks for the input.

why are you removing it? If it doesn't work, you got nothing to lose by cutting the wires, since they do nothing for you to begin with.


If you need to reuse it, then ignore what I said or leave enough wire so you can reconnect them later.

If you don't have access to a torch you may try the following:

Apply a penetrating solution to the sensor threads such as Kroil or a 50/50 mixture of power steering fluid and acetone. Saturate with the penetrating solution and vibrate the fitting by hitting it lightly with a 1 lb hammer for several minutes. Let set for several hours or overnight.

Cut the oxygen sensor wire and apply the appropriate closed-end wrench to the oxygen sensor, the longer the wrench the better. Hit the free end of the wrench with a 2 to 4 lb hammer in the proper direction to untighten the threads so as to loosen the sensor.

It throws an intermittent code. Usually when it's cold. I'm guessing the internal heated resistor is bad. Where it's at, there isn't room for a closed end wrench without taking the heat shield off.

Use a commonly available specialty offset o2 sensor socket that has a 1/2" drive offset cast into it. Sort of a crowfoot idea. Way better that cutting up an old socket and maybe getting it out. The heat will definitely help though.