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O2 Sensor differences?

Uncle_Enzo

NAXJA Forum User
I did some searching and haven't been able to find an answer.


Are the actual sensor parts of of the upstream and downstream O2 sensors the same and is it just the wire harnesses and connectors that are different?



I found NTK O2 sensors part numbers for my 1999 XJ sport:


23151 upstream

23099 downstream


I bought the 23099 cheap on amazon. 23151 looks like it has been discontinued. Local Autozone, Napa, and Orielly's sell the 23151 for 70-80 bucks before everyone runs out vs 30ish on amazon for the 23099.



Can I just buy another 23099 and wire with the correct pins to the upstream harness from the wiring diagram info? I'm pretty handy with a soldering iron.



I have a Free America XJ smog wise. Someone else was nice enough to import it to Kalifornia for me before I bought it. Some jackasses stole my catalytic converter last March. Now it is time for some government and have get a smog inspection. (Despite said nice importer paying a 300 smog impact fee because out of state vehicles produce more smog.) I have to replace at least my downstream sensor. (no way is that thing is coming out without breaking it) Besides the fact that, both O2 sensors on look original and I'm not sure how trustworthy they still are. It sounds like a happy fantasy to get more than 13mpg on my stock rig. Perhaps new O2 sensors will help.



If I can't use a 2nd downstream sensor, is it ok to mix Denso or some other OEM brand upstream sensor with my NTK downstream sensor?
 
The sensors are the same except for the pigtail length. I believe the the front O2 pigtail needs to be longer than the rear O2, so a rear O2 may not work. With that said, when I picked up an NTK rear O2 sensor for my 2000 XJ, the pigtail was significantly longer than the one it replaced, so it probably would have worked at the front too. Bottom line is that I think you'll need to measure.
 
The sensors are the same except for the pigtail length. I believe the the front O2 pigtail needs to be longer than the rear O2, so a rear O2 may not work. With that said, when I picked up an NTK rear O2 sensor for my 2000 XJ, the pigtail was significantly longer than the one it replaced, so it probably would have worked at the front too. Bottom line is that I think you'll need to measure.

I forget what I replaced in my 2000 XJ, but the MOPAR was shorter wiring than the Aftermarket wiring. I think the CPS. The pigtails are different between the front and the rear.
I did replace the front with a DENSO and the Rear with a NTK. I might go back and re-replace the front with an NTK.
 
I did replace the front with a DENSO and the Rear with a NTK. I might go back and re-replace the front with an NTK.




Do that sooner than later because a few sites are marking the upstream NTK 23151 as discontinued. They might be out of stock everywhere soon.


Thanks for the info folks. I'll let you know how it turns out after my smog check.
 
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