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2004 chevy trailblazer_lt_ext
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Discussion Starter · #1 ·
Has anybody solved how to disconnect the downstream O2 from it's connector? Mine's located above the exhaust pipe towards the engine. Trying to unclip it from the harness looks near impossible because you cannot see it and would have to unclip it one-handed. Is it accessible from the front passenger wheel well?
 

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2002 Pewter ls with automatic trans. 4x2, gray cloth interior.
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I have a Cal cat and replaced both O2 no issue. Not sure if the downstream location is different for non Cal cats hmm.

Only issue I had was trying to zip tie the cable.
 

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2004 chevy trailblazer_lt_ext
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Discussion Starter · #3 ·
on 10/31, I did get help to get the downstream O2 Sensor out. My neighbor heated it with his MAP gas torch, then I put my O2 socket on a 1/2" breaker bar and it cracked. He gently worked a wrench to ease the sensor out (one half turn to the left and a quarter turn to the right--repeat until it's out. We did not run into stripped threads--probably because we went very slow easing it out.

So far so good---my neighbor tested the new sensor with his OBD reader and it was functioning good. For $60, help from a good neighbor and a little MAP Gas, my "check engine" light is now gone. I will be replacing the upstream sensor as soon as I replace my daughter's brakes (she has a Ford Edge).

I heard from others that the best time to remove an O2 sensor is when the engine's hot. I went for a ride today and tested the temperature of the O2 with an infrared reader. It was about 250 degrees F. I think I'll be ok removing it slowly when it's that hot.
 

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2003 chevy trailblazer_ltz
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on 10/31, I did get help to get the downstream O2 Sensor out. My neighbor heated it with his MAP gas torch, then I put my O2 socket on a 1/2" breaker bar and it cracked.
You got lucky.

1. There is no such thing as "MAPP gas" any more. Hasn't been for ten years or more. What is now sold is "MAP-Pro" which is chemically-different, not as hot as the old, genuine "MAPP" gas.
2. In any event, without supplemental oxygen, Propane, MAPP, or MAP-Pro is usually not hot enough to do any good. Add a bottle of oxygen and the proper hoses/torch, or just use Oxy-Acetylene, and you have enough heat.
3. O2 sensor sockets REALLY SUCK for removing most O2 sensors. They're split along one side for clearance for the wire harness. The spit opens up at high torque, then the socket slips on the wrenching flats of the sensor. O2 sensor sockets are fine for installing sensors, not removing them. When O2 sensors are difficult to remove (most of them...) I use a 7/8 six-point combination wrench (box-end) or a 7/8 deepwell impact socket, using either the actual impact wrench or a breaker bar/long-handle ratchet and a cheater pipe. Using the deepwell impact socket requires clipping the wire(s) off the sensor; and you need a deepwell socket that has room inside for the O2 sensor body. Many/most deepwell sockets are reinforced inside, the sensor body won't clear the inside of the socket. I bought a Wright socket for O2 sensor work.

Wright is a family-owned company making tools in the USA. VERY recommended.

4. It is sometimes necessary to remove the pipe, for tool clearance to get the O2 sensor out. Yeah, that really sucks. I blame the engineers for utterly failing to provide enough wrenching surface and tool clearance on the sensors; and for not assuring that the threads won't seize in extended use. (i.e., it was crazy to standardize on 7/8" hex on the sensor, they should have been a full inch, maybe an inch-and-a-quarter; even if the thread size was the same-ol'-ordinary 18mm like the old Ford and Chrysler spark plugs; and the threads in the exhaust system and on the sensor need something more than just a light coating of anti-seize.)
 

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Discussion Starter · #5 ·
You got lucky.

1. There is no such thing as "MAPP gas" any more. Hasn't been for ten years or more. What is now sold is "MAP-Pro" which is chemically-different, not as hot as the old, genuine "MAPP" gas.
2. In any event, without supplemental oxygen, Propane, MAPP, or MAP-Pro is usually not hot enough to do any good. Add a bottle of oxygen and the proper hoses/torch, or just use Oxy-Acetylene, and you have enough heat.
3. O2 sensor sockets REALLY SUCK for removing most O2 sensors. They're split along one side for clearance for the wire harness. The spit opens up at high torque, then the socket slips on the wrenching flats of the sensor. O2 sensor sockets are fine for installing sensors, not removing them. When O2 sensors are difficult to remove (most of them...) I use a 7/8 six-point combination wrench (box-end) or a 7/8 deepwell impact socket, using either the actual impact wrench or a breaker bar/long-handle ratchet and a cheater pipe. Using the deepwell impact socket requires clipping the wire(s) off the sensor; and you need a deepwell socket that has room inside for the O2 sensor body. Many/most deepwell sockets are reinforced inside, the sensor body won't clear the inside of the socket. I bought a Wright socket for O2 sensor work.

Wright is a family-owned company making tools in the USA. VERY recommended.

4. It is sometimes necessary to remove the pipe, for tool clearance to get the O2 sensor out. Yeah, that really sucks. I blame the engineers for utterly failing to provide enough wrenching surface and tool clearance on the sensors; and for not assuring that the threads won't seize in extended use. (i.e., it was crazy to standardize on 7/8" hex on the sensor, they should have been a full inch, maybe an inch-and-a-quarter; even if the thread size was the same-ol'-ordinary 18mm like the old Ford and Chrysler spark plugs; and the threads in the exhaust system and on the sensor need something more than just a light coating of anti-seize.)
Thanks for the tool tip and the info. I agree I was lucky...things could have gotten bad---so glad I didn't have to deal with stripped out threads. My hope is that the new ACDELCO downstream will be the last one I have to replace.Happy Thanksgiving, Sir!
 
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