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(2002 Toyota Previa/Estima/Tarago ACR30, engine 2AZ-FE)

One of my two pre-cat O2 sensors is faulty. The garage I put the car in did not manage to replace it - they told me it is stubborn and that even after applying heat (acetylene burner) it did not come off. They were able to turn it only a bit and than it stopped.

They did not want to apply brute force as the thread in the exhaust manifold could be stripped.

I believe they were kind of in a hurry (I asked them to replace the sensor after finishing a long list of jobs and they already had other cars ordered in), so they may have not applied any kind of penetrating oil.

My question is - am I in a danger of stripping the manifold thread if I apply extensive force on the sensor (provided that I won't strip the sensor's hex head)?

EDIT 2017-10-08: After a day of spraying the O2 sensor with WD-40 Specialist Penetrant, I set myself to remove the sensor. Took me about an hour of slow work with 22 box wrench, vice grip and a hammer (I didn't remove the heatshield). The thread of the old sensor was indeed stripped (well, to be precise, its outside half), so the material must have remained in the exhaust manifold's thread.

Then came the worse part of the job - reviving the thread with a tap. I went really slow and after basically three passes I was able to rotate the tap by hand. Tried inserting the new O2 sensor but when I started to feel the resistance, I removed it and decided to first screw another old O2 sensor into the manifold - for case I damage its thread. I really wasn't sure but had basically nothing to lose so I applied more force and finished screwing the sensor. Ran the engine for a while to test it does not leak. Everything was surprisingly OK so I removed the old sensor and now only had to put the new one in. After couple of minutes, voilà, it was there :)

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If they told you the truth and unsuccessfully tried an acetylene burner:

Well, yes: What does not get loose with such measures will (most likely) damage the thread (if that not already happened) if you force the sensor out.

I personally would go that path:

  1. Soak the thread with penetrating fluid and buy a matching helicoil/thread-repair kit.
  2. When you feel secure: Drive around so the manifold gets hot, cut the sensor cable, apply additional heat and use a good ring wrench on the sensor (only possible when you cut the cable).
  3. Should it go out fine: Good
  4. Otherwise: Repair the thread
  5. Use anti-seize when installing the new sensor

Should you not feel confident enough to repair the thread: There are matching weld-on rings available. A good repair/machine shop should be able to fix that.

  • Clear set of options - good. – Solar Mike Oct 5 '17 at 10:29
  • Well, there are some heat marks around the sensor (including the sensor itself) but they definitely have not removed the heatshield which probably caused them not to heat it properly (manifold only). I also have not spotted any tracks of using penetrating oil when I first looked at the engine. I have applied two batches of WD-40 Specialist penetrating oil, first one yesterday evening, second one this morning. Hopefully it will come off when I try it in the evening :) – MaSlo Oct 5 '17 at 12:01
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    It may be worth a few applications of penetrating fluid over several days, I've seen things finally twist off after a week of spraying. Also, giving it a tap or two with a hammer can sometimes loosen things up - not the sensor, tap the base where the sensor screws into, a punch will give you the precision you need. – GdD Oct 5 '17 at 13:15
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I don't want to hijack the answer from Myself, but I do want to submit a photo. I recently had to work on a stuck Heated Exhaust Gas Oxygen (HEGO) sensor. I had been attempting to use a friends Snap On branded adapter (basically a large socket with a slot in it for the wiring) and I just couldn't get the tool to fit easily. The socket was just too long. I tried using a variety of wrenches and crows foot adapters. Nothing would work. I ended up borrowing one of these from the Autozone free tool loaner program. (Autozone has a program in many places that essentially sell you the tool, then give you a FULL refund if you return it within 60 days...Great program for tools you use once every three years...)

This tool was way awesome. You could easily apply a whole lot of torque on the sensor. It was beefy and well built.

Oxygen Sensor Wrench

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I own a 4 cylinder 2003 Camry. I needed to change the oxygen sensor on it.

I first removed the heat shield. The two halves are held on by screws. The top half removes easily. The bottom half as well except it has a hole in it where the wire for the oxygen sensor connects. If you look on You Tube there are several videos as to where the wire to the oxygen sensor connects. Once you disconnect the wire you can feed it through the hole in the bottom half of the heat shield.

I didn't spray the oxygen sensor but the shallow "well it sits in with PB Blaster. I took a deep socket of proper size and slipped it over the oxygen sensor and tapped it as instructed. (Don't hit it too hard) and waited.

It took three or four applications and some time before it became loose. Sometimes you can try to turn the oxygen sensor (or any tight bolt for that matter) as if you were tightening it. Don't use too much force. Sometimes that little turn the other way will "break" the rust free.

I would suggest using a box wrench to loosen the oxygen sensor. My personal opinion is the box wrench will give you a more positive grip on the oxygen sensor so you don't round it off.

Just remove it and make sure you get an exact replacement. Use what is called a never seize compound on the threads. Only a small dab away from the face of the oxygen sensor, If you get any of the never seize on the face of the oxygen sensor, its ruined.

Reinstall the sensor. Connect the bottom half of the heat shield. Run the wire through the heat shield and up to where it connects. Reinstall the upper portion of the heat shield. Start the car. Let it idle for a bit. If the warning light stays on go to a place like Auto Zone. They have an engine analyzer that can be used reset the warning light. If it goes off and stays off give yourself a pat on the back.

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