The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread

I've been having pretty consistent fuel or possibly exhaust related issues; high idling, low idling, poor fuel efficiency (relative to what I usually get), and long starting times.

I have cleaned my IAC (idle air control), replaced the CPS (crankshaft position sensor), and replaced the TPS (throttle position sensor). Which didn't fix anything.

So, today I tested the resistance on all of my oxygen sensors:
  • Bank 1
    • Sensor 1: 5.3 ohms
    • Sensor 2: 5.1 ohms
  • Bank 2
    • Sensor 1: 4.5 ohms
    • Sensor 2: 4.8 ohms
As I understand it, 5 to 7 ohms is what i'm looking for, correct? It appears both my bank 2 sensors are bad?

Thank y'all!
 
I've been having pretty consistent fuel or possibly exhaust related issues; high idling, low idling, poor fuel efficiency (relative to what I usually get), and long starting times.

I have cleaned my IAC (idle air control), replaced the CPS (crankshaft position sensor), and replaced the TPS (throttle position sensor). Which didn't fix anything.

So, today I tested the resistance on all of my oxygen sensors:
  • Bank 1
    • Sensor 1: 5.3 ohms
    • Sensor 2: 5.1 ohms
  • Bank 2
    • Sensor 1: 4.5 ohms
    • Sensor 2: 4.8 ohms
As I understand it, 5 to 7 ohms is what i'm looking for. Therefore, I need to replace both my sensors on bank 2 - perhaps even replace all of them for good measure?

Thank y'all!

Yes, replace them, and replace ALL of them. I think it's stupid when people replace one O2 sensor and not all of them. O2 sensors are regular wear and tear maintenance items and should generally all be replaced around 80k miles, regardless of whether or not they are bad. It will keep your engine running good.
 
Yes, replace them, and replace ALL of them. I think it's stupid when people replace one O2 sensor and not all of them. O2 sensors are regular wear and tear maintenance items and should generally all be replaced around 80k miles, regardless of whether or not they are bad. It will keep your engine running good.

My good sir, you always are online responding to "calls for help" from forum members. I certainly imagine I am not alone when I exclaim how much I appreciate this forum!

Is the "ohms test" a solid identifier of a bad o2 sensor? I just am not well versed in testing components such oxygen sensors.
 
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My good sir, you always are online responding to "calls for help" from forum members. I certainly imagine I am not alone when I exclaim how much I appreciate this forum!

Is the "ohms test" a solid identifier of a bad o2 sensor? I just am not well versed in testing components such oxygen sensors.

The ohms test is a solid example of a bad O2 sensor, an O2 sensor that is starting to go bad, yes.

And no problem, I spend a lot of time online these days, so I'm always happy to help out :)
 
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Hello everyone. I have been reading this forum for a long time. Thanks for all the posts. It's help me so many times. This is my first post. I have been chasing a P0431 and now P0421 code for about a year. I have replaced O2 sensors with NTK sensors (All 4) and new pacesetter cat set because of an original cat blown out and and code. Still have codes after replacing cats. I am also getting 8 mpg. A side note: The flanges seem to loosen from time to time and I tighten them (code still comes back after tightening even though it sounds better or more "sealed"). The factory bolt and clip/nut combos don't seem to do the trick. Even with brand new ones. I have also added an extra mounting point from the passenger side of the engine for the exhaust piping. Finally gave up and took it to the stealership (only because I was going for the the clutch switch recall) and they said I need all new Mopar O2 sensors and factory cats ($2500). Um... I don't think so. They said that NTK won't work. Is there some truth to this? I have contacted pacesetter and they are sending me a new cat set under warranty. Yippy! The Y pipe didn't fit right when I first installed it. I think that may have been the problem all along. Pacesetter said it might be a defect and the Y pipes were taken out of the weld mold before it was all the way cooled. Has this happened to anyone else? Has anyone else found a better way to bolt the flange on? There is almost no room to not use the clips from when I see. I tried to get extra (thin) nuts on top but also no room. Thank you so much.
I just wanted to reply to this after replacing the catalytic converter AGIAN. I called Pacesetter. I have been in contact with them since I installed it. I had done a few test for them. They finally agreed to send me a new one under warranty. The flanges lined up perfectly this time and I had a buddy help me install. I used new original bolt and then lock flange nuts and a lock washer on top. Torqued to 22ftlb. It pressed in very nicely to the ball flanges but took a while with the back and forth on 4 bolts, however the pipe coming down and around was not lined up straight back. It also awfully close to the oil pan on the driver side as it comes down. So there is now a leak at the muffler flanger. I had to finished up as it was getting dark so we lined it up the best we could. I'm going to carefully take a floor jack to it later to push it up. It is well after the O2 sensors so it shouldn't affect the CEL codes. In the end after a week the codes have vanished. In my opinion pacesetter took the Y flange out of the weld jig too soon and it cooled and warped. DON'T purchase the pacesetter 324236. Even though it ever up ok in the end I think. Here was another review that said they don't line up on quadratec after I bought it. The emissions still say Not Ready so I have to do the TSB that the dealership wouldn't do. Even though it's under warranty I'm gonna tackle it myself. That Jeep dealership is the worst in South Florida.
 
I replaced my O2 sensors today and things really went smoothly thanks to this thread and website in general. I was expecting trouble with these sensors. I live in the northeast and have had some issues taking apart rusted up parts so was expecting the worst. But I sprayed, no I saturated, them with Kroil last weekend, again in the middle of the week and last night. They all came off easily. Thanks to @Chris and everyone who contributes.
 
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What are Bank 1, Bank 2, etc.?
Since this question pops up from time-to-time, here's an easy to follow diagram that illustrates what they mean when your OBDII code scanner (or manual) tells you something like "O2 sensor, Bank 1, Sensor 2":

View attachment 12208


What does upstream and downstream mean?
Simple, upstream means the O2 sensor is "upstream" of the catalytic convertors, meaning before the catalytic convertors. Downstream means the O2 sensor is "downstream" of the catalytic convertors, meaning after the catalytic convertors.


What brand of O2 sensors should I use for replacements?
Pay close attention to this one so you can do it once and do it right! The Jeep Wrangler TJ is extremely sensitive to all oxygen sensors other than NGK / NTK. Bosch O2 sensors and all the others (including the crappy Chinese brands you'll buy at your local auto part store) are very well documented as not working properly with our TJs. In other words, you plug them in and you assume all is well, until you notice your check engine light isn't going away. This is almost always due to the fact that you didn't use an NGK / NTK replacement O2 sensor.


Okay, so why don't other sensors (i.e. Bosch) work on our Jeeps?
Glad you asked! Check out this video for a detailed explanation of why other brands of O2 sensors don't work on our TJs:



So which O2 sensors do I need?
I'm going to break down which sensors you need based off what year your TJ is. The part numbers (and information) below were taken directly from the NGK website, so you can assure it is 100% accurate (even double checked each individual year and model before writing this thread).


4 Cylinder Engines
1997-2000
NGK #23506 - Bank 1, Sensor 1 (Upstream)​
NGK #23151 - Bank 1, Sensor 1 (Upstream) (1998 ONLY)​
NGK #23099 - Bank 1, Sensor 2 (Downstream)​
2001-2004
NGK #23138 - Bank 1, Sensor 1 (Upstream)​
NGK #23141 - Bank 1, Sensor 2 (Downstream)​
2005-2006
NGK #23159 - Bank 1, Sensor 1 (Upstream)​
NGK #23159 - Bank 1, Sensor 2 (Downstream)​
6 Cylinder Engines
1997-1999
NGK #23151 - Bank 1, Sensor 1 (Upstream)​
NGK #23099 - Bank 1, Sensor 2 (Downstream)​
2000
NGK #23122 - Bank 1, Sensor 1 (Upstream)​
NGK #23506 - Bank 2, Sensor 1 (Upstream)​
NGK #23099 - Bank 1, Sensor 2 (Downstream)​
NGK #23099 - Bank 2, Sensor 2 (Downstream)​
2001-2003
NGK #23139 - Bank 1, Sensor 1 (Upstream)​
NGK #23138 - Bank 2, Sensor 1 (Upstream)​
NGK #23142 - Bank 1, Sensor 2 (Downstream)​
NGK #23141 - Bank 2, Sensor 2 (Downstream)​
2004
NGK #23137 - Bank 1, Sensor 1 (Upstream)​
NGK #23135 - Bank 2, Sensor 1 (Upstream)​
NGK #23132 - Bank 1, Sensor 2 (Downstream)​
NGK #23531 - Bank 2, Sensor 2 (Downstream)​
2005-2006
NGK #23018 - Bank 1, Sensor 1 (Upstream)​
NGK #23160 - Bank 2, Sensor 1 (Upstream)​
NGK #23159 - Bank 1, Sensor 2 (Downstream)​
NGK #23158 - Bank 2, Sensor 2 (Downstream)​
Misc Installation Notes
When installing new O2 sensors, be certain to use some anti-seize on the threads of the new O2 sensors! This is important, and will save you a huge headache should you ever need to remove them in the future.

In addition, a O2 sensor socket will greatly aide in the installation and removal of O2 sensors. I recommend this one.


First of all thanks for posting this and being so detailed.

Can you please confirm that the following is the right part number for 2005 LJ 4.0l 6 speed:

NGK #23159 - Bank 1, Sensor 2 (Downstream)

Tried to buy from amazon and said it didn’t fit my Jeep...
 
First of all thanks for posting this and being so detailed.

Can you please confirm that the following is the right part number for 2005 LJ 4.0l 6 speed:

NGK #23159 - Bank 1, Sensor 2 (Downstream)

Tried to buy from amazon and said it didn’t fit my Jeep...

No problem!

That is the correct part number. Don't always trust Amazon, they've been wrong a number of times before.
 
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Thanks for updating this. I am getting ready to change all of my o2 sensors on my 2004 as preventative maintenance...chasing down a rough idle and slow start condition (replaced other applicable sensors and cleaned/changed IAC and throttle body as well as plugs to no avail)... Not throwing any codes at present. Engine seems to have good power, no hesitation, getting 11-13mpg in town. Thinking I should buy a relay too since they are cheap.

My TJ has 52k on it. Wondering if I should change the pre-cats while I am down there. The flowmaster with the pre-cats and 3rd cat is only $250. Which is way cheaper than the Eastern one... Unless I am missing something.

Oh and @Chris - Thanks so much for this and all the other informative threads. So many of us would be lost without everything you've done...
Have you installed the flowmaster cats. This is part of my next project, including replacing rear main seal and bent oil pan. Dred those exhaust bolts. Probably going to run down a six point wiggle joint.
 
Have you installed the flowmaster cats. This is part of my next project, including replacing rear main seal and bent oil pan. Dred those exhaust bolts. Probably going to run down a six point wiggle joint.
Actually no I haven’t. I just changed the O2 sensors this morning. All 4 of them. I used the NGK. Anyway I decided to try just the O2 sensors first before I do more. And likely when I do change the cats I will have a muffler shop do everything including the cats and everything rearward.

I have not even driven the Jeep to see if the O2 sensors helped. But I’m planning on taking a ride in a little while.

My takeaways from the process of changing the O2 sensors. Be patient and don’t get in a hurry. Have all the stuff you need including the sensor socket, breaker bar or large ratchet (I used a torque wrench), small wire ties, crescent wrench, medium flat head screwdriver (helps with the electrical plugs), extensions (15” used for the two upstream sensors). They are all very doable, just a puzzle figuring out how to best get the tools where they need to go with the suspension and steering components in the way (downstream sensors) and the multitude of things in the way for the upstream ones. The worst sensor to get to was the upstream front one. The worst electrical plug is the one for the downstream back one which is behind the head on top of the tranny. But you can get to it ok from the top. Anyone under 5’10” or has 3in or more of lift could do with a stool or something to get a good access.

Be very sure you are looking at the diagrams right to figure out which sensor (part number) goes where. Check the electrical plugs to be sure they fit before screwing the sensor in. If it doesn’t fit you were looking at the diagram wrong/have the wrong sensor in your hand. I screwed this up not once but twice on one sensor and once on another. Nothing like having to do things twice, or thrice. Even with that the whole project took just over an hour and that included getting all the tools out and putting them all away.
 
Last edited:
What are Bank 1, Bank 2, etc.?
Since this question pops up from time-to-time, here's an easy to follow diagram that illustrates what they mean when your OBDII code scanner (or manual) tells you something like "O2 sensor, Bank 1, Sensor 2":

View attachment 12208


What does upstream and downstream mean?
Simple, upstream means the O2 sensor is "upstream" of the catalytic convertors, meaning before the catalytic convertors. Downstream means the O2 sensor is "downstream" of the catalytic convertors, meaning after the catalytic convertors.


What brand of O2 sensors should I use for replacements?
Pay close attention to this one so you can do it once and do it right! The Jeep Wrangler TJ is extremely sensitive to all oxygen sensors other than NGK / NTK. Bosch O2 sensors and all the others (including the crappy Chinese brands you'll buy at your local auto part store) are very well documented as not working properly with our TJs. In other words, you plug them in and you assume all is well, until you notice your check engine light isn't going away. This is almost always due to the fact that you didn't use an NGK / NTK replacement O2 sensor.


Okay, so why don't other sensors (i.e. Bosch) work on our Jeeps?
Glad you asked! Check out this video for a detailed explanation of why other brands of O2 sensors don't work on our TJs:



So which O2 sensors do I need?
I'm going to break down which sensors you need based off what year your TJ is. The part numbers (and information) below were taken directly from the NGK website, so you can assure it is 100% accurate (even double checked each individual year and model before writing this thread).


4 Cylinder Engines
1997-2000
NGK #23506 - Bank 1, Sensor 1 (Upstream)​
NGK #23151 - Bank 1, Sensor 1 (Upstream) (1998 ONLY)​
NGK #23099 - Bank 1, Sensor 2 (Downstream)​
2001-2004
NGK #23138 - Bank 1, Sensor 1 (Upstream)​
NGK #23141 - Bank 1, Sensor 2 (Downstream)​
2005-2006
NGK #23159 - Bank 1, Sensor 1 (Upstream)​
NGK #23159 - Bank 1, Sensor 2 (Downstream)​
6 Cylinder Engines
1997-1999
NGK #23151 - Bank 1, Sensor 1 (Upstream)​
NGK #23099 - Bank 1, Sensor 2 (Downstream)​
2000
NGK #23122 - Bank 1, Sensor 1 (Upstream)​
NGK #23506 - Bank 2, Sensor 1 (Upstream)​
NGK #23099 - Bank 1, Sensor 2 (Downstream)​
NGK #23099 - Bank 2, Sensor 2 (Downstream)​
2001-2003
NGK #23139 - Bank 1, Sensor 1 (Upstream)​
NGK #23138 - Bank 2, Sensor 1 (Upstream)​
NGK #23142 - Bank 1, Sensor 2 (Downstream)​
NGK #23141 - Bank 2, Sensor 2 (Downstream)​
2004
NGK #23137 - Bank 1, Sensor 1 (Upstream)​
NGK #23135 - Bank 2, Sensor 1 (Upstream)​
NGK #23132 - Bank 1, Sensor 2 (Downstream)​
NGK #23531 - Bank 2, Sensor 2 (Downstream)​
2005-2006
NGK #23018 - Bank 1, Sensor 1 (Upstream)​
NGK #23160 - Bank 2, Sensor 1 (Upstream)​
NGK #23159 - Bank 1, Sensor 2 (Downstream)​
NGK #23158 - Bank 2, Sensor 2 (Downstream)​
Misc Installation Notes
When installing new O2 sensors, be certain to use some anti-seize on the threads of the new O2 sensors! This is important, and will save you a huge headache should you ever need to remove them in the future.

In addition, a O2 sensor socket will greatly aide in the installation and removal of O2 sensors. I recommend this one.

Hey Chris. I think if you added this link -

https://partcat.com/ngk

- to your original post, it would reduce the number of repeat questions on this thread. That's the part finding webpage directly from NKG.

Also, I think adding something along the lines of "if your old sensors won't budge, add some heat to them from a MAPP gas torch or something similar to help remove them." I had to use MAPP gas on my downstream sensors to get them out.
 
Hey Chris. I think if you added this link -

https://partcat.com/ngk

- to your original post, it would reduce the number of repeat questions on this thread. That's the part finding webpage directly from NKG.

Also, I think adding something along the lines of "if your old sensors won't budge, add some heat to them from a MAPP gas torch or something similar to help remove them." I had to use MAPP gas on my downstream sensors to get them out.

Great advice, I’ll definitely add this to the original post!
 
Ordered two upstream sensors (23018 and 23160) for 2006 4.0
Is there a way to tell them apart once they out of the package?
I took both out, aaaaaand kinda forgot which came from which box lol. Both look identical, one stamped 0ZA623-C1 and other is 0ZA623-C2
 
Ordered two upstream sensors (23018 and 23160) for 2006 4.0
Is there a way to tell them apart once they out of the package?
I took both out, aaaaaand kinda forgot which came from which box lol. Both look identical, one stamped 0ZA623-C1 and other is 0ZA623-C2
Don’t worry about it. When you go to change them, take the first old one off your Jeep and compare the plugs closely. There are three notches/keys on each plug. All 4 on your Jeep are different (notches in different places). So match up the notches and you will know...
 
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Update...

Changed all four O2 sensors.
Codes are back.
Loss of power with misfires.
Changing cats and while at it exhaust manifold.

Let’s see if it works.


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