O2 Sensor - HALP (1 Viewer)

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Joined
Mar 22, 2021
Threads
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Location
Nor Cal
Background - 2004 LX 470 205k miles

Got my first CEL a few months ago and it was the pass side bank 3 sensor. I had several other projects going on so it wasn't being driven much, but finally got around to replacing all 4 sensors. Rented an O2 socket, and replacements went off without a hitch.

Finished most of my projects last week and cleared CEL codes and drove the LX around for the first time in a while. After about 15 miles CEL/vsc lights go off. Plug in the OBDII and now I'm getting P0420.

Did some research on P0420 and understand this can mean many things that techstream could best diagnose. Went under the truck first to do a visual inspection on the upstream driver side sensor and see if I could find any glaring problems. Immediately I knew I had one. I had a new 22mm wrench that miraculously could give me some leverage down there and noticed I was not getting anywhere close to the amount of leverage I need to get this thing off - this was very confusing to me as when I did the replacement they came on and off so easily.

Finding ways to get more leverage I rented the same O2 socket to get back to work with a normal socket wrench - still not enough leverage and now I'm really worried and confused. Lifted the truck and got a breaker bar on it and still not enough leverage. Now I know something is completely screwed up with the threads.

Used a different O2 socket and started getting some play after rocking the socket clock wise and counter clockwise and finally got it out. None of this felt good at all. Brand new O2 sensor is below and you can see the mangled threads.

Other piece of possible useful info is that I did use antiseize when I replaced these. I thought I saw a forum use antiseize for O2 replacement here on MUD but maybe I was mistaken - not sure if that's relevant info or not. Other info is that these are OEM equiv denso O2's ordered from sparkplugs.com

Wondering in general how screwed I am and/or any solutions I might have at my disposal. Am I already looking forward to retapping the female threads in the upstream sensor if that's even at all possible?

Thanks in advance for any help/advice. This is definitely the most worried I've ever been.

IMG-1105.jpg
 
Please correct me if I am wrong:
P0420 is for a catalytic converter below threshold code. This code is generated when the rear sensor (Oxygen sensor, after the cat) find an issue with the catalytic converter. The sensor you removed is the air to fuel ratio sensor which is used to control the fuel trims:

Did you use an OEm or DENSO sensor?
 
You could try chasing the threads and see if you're able to clean them up, if that doesn't work, (and it doesn't look like it will, those are pretty hammed), then get a new sensor. I'd chase the threads on the pipe bung too just so you're not cross threading. If those are buggered up too an exhaust shop could weld in a new bung for you pretty easily.
 
Please correct me if I am wrong:
P0420 is for a catalytic converter below threshold code. This code is generated when the rear sensor (Oxygen sensor, after the cat) find an issue with the catalytic converter. The sensor you removed is the air to fuel ratio sensor which is used to control the fuel trims:

Did you use an OEm or DENSO sensor?
No you're not wrong. Indeed what you say regarding P0420 is the same readout I'm getting. Could've sworn I read on MUD someone getting this code and then focusing on Bank 1 upstream sensor. Would make sense that below threshold converter would be read at the downstream sensor.

Here's the sensor used. It is Denso, but to my knowledge this is the same one used for OEM.

Denso 234-4138 OE Identical Oxygen Sensor​

SKU #234-4138
ITEM #DEN234-4138
POSITION(S) UPSTREAM
BRAND DENSO
 
You could try chasing the threads and see if you're able to clean them up, if that doesn't work, (and it doesn't look like it will, those are pretty hammed), then get a new sensor. I'd chase the threads on the pipe bung too just so you're not cross threading. If those are buggered up too an exhaust shop could weld in a new bung for you pretty easily.
Thanks so much for the advice @Trunk Monkey. Refreshing to know that's an option
 

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