2008 Trailblazer O2 Sensor Success, Rust Belt

[wormwood1978]

I had some struggles with removing the upstream O2 sensor even after reading how others on this forum had successes and failures, so I wanted to share my experience.

2008 Trailblazer, 92,000 miles all in Maine and Michigan. Original sensor.

The sensors was operating good but I thought with the age and miles, it would be good to replace it now before it went bad and perhaps became more seized than it was probably already.

One week ago, I sprayed some PB Blaster on it. Yesterday, I removed the wheel for better access and left the O2 electrical connector in place in case I could not remove it and needed more time to come up with a better plan. I sprayed some PB blaster on it. I heated the car up for 10 minutes and used a temp gun to check the temp around the sensor (400 degrees). I used a moderate amount of force using a breaker bar and the O2 socket and it would not budge. I did not want to put a ton of force on it and perhaps bugger the threads. I then used propane to heat the area up to about 650 degrees, still no go. I sprayed some PB blaster on it again and two more times including before I went to bed.
The following morning, more PB Blaster an hour before. Warmed the car for 2 minutes bringing the temp around the sensor up to 300 degrees. Still would not budge. I then heated the area with the propane torch for probably 5 minutes. Moderate amount of force and it popped loose. Had I not had success, my plan was to order a bottle of Mouse Milk off of Amazon and try that as a penetrating oil. I also considering melting candle wax as well as an option if need be.

The Oxygen sensor socket I used was a 7/8” ½” drive, Autocraft AC830 with a 24” breaker bar.

I got the AC Delco Sensor (12592591) on a wholesaler sale on Rockauto for $26.79.

 

[sashainwy]

Thanks for sharing, it's very useful info. I'm going to replace mine as my scan tool is showing the sensor intermittently reports 0% 0V on that sensor. I'll check for bad wires first of course...

 

[mrrsm]

THIS is a Procedure that should NEVER be Attempted:

(1) NEVER Spray ANY Chlorinated, Fluoro-Hydro-Carbon Solvent on HEATED Components.
(2) At 900 Degrees Fahrenheit, these Solvents will decay and produce PHOSGENE GAS.
(3) If only ONE WHIFF of this Stuff does NOT Kill You Outright... it can Cripple you for Life.
(4) ALL of this Information is already available on the Spray Can Warning Labels.
(5) READ ALL WARNING LABELS PRIOR TO ATTEMPTING THE APPLICATION OF FLAME.

Chlorinated Brake Cleaner: Welder Beware - Outside Groove

Scott Wylie had passed out. He inadvertently created a poisonous gas from the chlorinated brake cleaner he used to prepare his parts.

outsidegroove.com

Phosgene - Wikipedia

en.wikipedia.org

The Silent But Deadly Inhalation Risks That HVAC Mechanics and Installers Face | HVAC School

If you intend upon using an Oxy-Acetylene or Propane Torch of any nature to Heat Up Fasteners and Base Metals that can and will INCANDESCENCE and therefore Ignite ANY local VOCs into a ready state of combustion... JUST USE THE TORCH!

Keep ALL Chlorinated Solvents and Flammable Materials well away from the Burning or Flame Work Environment. Often... Just HEATING UP the O2 Sensor and the adjacent Cast Iron of the Exhaust Manifold will be sufficient to Break Loose the Item when using the Proper O2 Sensor Sockets and Tools for this R&R.

 

[sashainwy]

Good reminder.

 

[jmonica]

I had some struggles with removing the upstream O2 sensor even after reading how others on this forum had successes and failures, so I wanted to share my experience.

2008 Trailblazer, 92,000 miles all in Maine and Michigan. Original sensor.

The sensors was operating good but I thought with the age and miles, it would be good to replace it now before it went bad and perhaps became more seized than it was probably already.

One week ago, I sprayed some PB Blaster on it. Yesterday, I removed the wheel for better access and left the O2 electrical connector in place in case I could not remove it and needed more time to come up with a better plan. I sprayed some PB blaster on it. I heated the car up for 10 minutes and used a temp gun to check the temp around the sensor (400 degrees). I used a moderate amount of force using a breaker bar and the O2 socket and it would not budge. I did not want to put a ton of force on it and perhaps bugger the threads. I then used propane to heat the area up to about 650 degrees, still no go. I sprayed some PB blaster on it again and two more times including before I went to bed.
The following morning, more PB Blaster an hour before. Warmed the car for 2 minutes bringing the temp around the sensor up to 300 degrees. Still would not budge. I then heated the area with the propane torch for probably 5 minutes. Moderate amount of force and it popped loose. Had I not had success, my plan was to order a bottle of Mouse Milk off of Amazon and try that as a penetrating oil. I also considering melting candle wax as well as an option if need be.

The Oxygen sensor socket I used was a 7/8” ½” drive, Autocraft AC830 with a 24” breaker bar.

I got the AC Delco Sensor (12592591) on a wholesaler sale on Rockauto for $26.79.

 

[jmonica]

Thanks for posting your experience. I realize this is a. Year old but it's appreciated. I'm about to attempt mine. I made a feeble attempt by spraying it with PB and a quick torch with map gas but not confident in the o2 wrench /socket I have, so I decided to wait until I received a new tool. Gonna get back to it this coming weekend and I'm afraid of it. If it was the downstream I wouldn't be as concerned. I do have a new exhaust manifold, but that's an even bigger job and the risk of snapping a bolt on that scares me even more.
So it seems that pb, warm it up, give it a few cranks on the breaker bar, soak it down again, let it sit over night, warm it up, blast it with heat, soak it down again, is the process that will give me the best chance.

I think heating it up before soaking it with pb might give the the PB a best chance to creep in but who knows.

I've tried the candle wax thing on other rusted nuts and bolts and never had success with it though I've been told it works. I think it depends on how welded with rust the threads are. If it can't creep into the threads, it's not going to do much.

Thanks again for posting your experience with removing the sensor.

On a side note, almost every video on YouTube is for the downstream sensor and many with the pipe out of the car. That's a totally different and easier situation than the upstream still in the vehicle in my opinion.

If I happen to have success removing it, I'll post what happened.

Now I'm trying to decide if I should take the plunge and just snip the wire off. If I knew it was definitely a dead sensor and I was confident I'm going to get it out, I wouldn't think twice about it but the sensor is the original and the engine has over 300k miles on it, so I'm really pessimistic I'm going to get it out on the first try.

I didn't think I needed to remove the wheel to access it because it looks like the sheet metal would still be in the way, but have to take a better look at it. If I have to bend or grind away a little steel to get a good angle on it, then so be it.

 

[budwich]

while you contemplate your removal process, you can practice getting your fingers up / at the connector to disconnect the sensor. That is fun. Of course, then you can practice reconnecting it.

On the sensor removal, hit it with significant heat at the "nut head" while you put an open ended wrench / vise grip in the freezer. Once heated, get the "freezing cold" wrench and put it to work. The "extra thermal shock" will likely to be successful at getting the thing off. It is my choice for stubborn bolts / nuts.

 

[Brian K]

Both sensors are working but I am getting a P0138 error every few weeks so figure it was time to replace as I have 175K on it so the sensors are probably getting lazy. I order 2 Denso sensors from RA. I tried doing O2 yesterday. Got the upstream one out and replaced with the deep socket slot type and a breaker bar, but the downstream one is a problem. The deep socket with the slot wouldn't fit because of the tranny and cooling lines so I got the crowfoot type. That didn't work either mainly because it seems, for some reason, my sensor head is a little smaller than 7/8" so it tended to want to round the sensor nut as I put pressure on it. I will try a 21mm box end and see if that fits but that will mean cutting the wires which I want to avoid until it is loose. I'll next try to heat with a MAP torch. I don't want to get too 'rammy' but perhaps a bigger hammer and pipe wrench will eventually be the solution. I have sprayed PB Blaster a few times but because the head is slightly smaller than the sockets, it wants to round. Finesse first, then a BFH!

 

[TollKeeper]

On the downstream one, I have always had the best luck just using a regular 6 sided wrench.

On my Aztek, I used the 6 sided wrench, and I had all my weight on that thing, and I heard a snap/crunch. Started cussing under my breath. But that was just the rust breaking, and it came out fine. YRMV.

 

[808]

I encourage you to bring a wire brush to the party, and scrub the dickens out of what can and will be liberated with the PB Blaster - the biggest obstacle to the penetration is surely going to be the oxide weld at the thread profile, and the more rust and charred road grit that can be liberated from the area is *absolutely* critical in getting your kroil/pb/pen. lube down into that port. Also, heating the exhaust pipe ------exclusively------ around the area of the o2 port is the name of/the aim of the game. Constant pressure on the fitting will be helpful as well, but sharp raps against the hex may be necessary - most importantly making sure you give yourself a backup "dog/restraint" so your exhaust pipe isn't swinging with every tap from your ballpeen/chisel/punch - do you have the special cut out socket? Heating the sensor itself is just going to make it bind harder to the interior of the port. @mrrsm has the name of the game set up for success at cancer free/lack of mortal peril advice - if you're not working with a heavy upstream fan pushing all your fumes away from you, I encourage you to bring that to the party. Also, have you looked at your fuel lines recently to ensure you've got no leaks if you're going to be torching?

 

[Mooseman]

Use a 22mm six sided deep socket. It's a little tighter on the sensor hex than the 7/8" sensor tools. I cut a slit in a 22mm impact socket for the wire and it doesn't even flex open like the other tools do. And you can use a 1/2" breaker bar on it.

 

[Brian K]

I got the DS sensor out finally. I had to use heat twice and used a pipewrench. I was ready to give up, then it just twisted out easily. A big surprise that it came out so I suspect the 2hd heat soak was the answer. Also a problem with the 'crowfoot' O2 removal socket and box end wrenches was that was that my sensor was slightly smaller than the wrenchs and the hex head wanted to round off . The pipewrench also got a good bite on it too. Connecting it back up was a PITA and longer fingers would have helped. O2 readings are much more stable now and no more codes so my guess at what caused the code in the first place was correct. Thanks for the advice in this and other posts about using heat. This forum is still a great source of info for us wanting to keep our old pals running well.