TheVet

Called and spoke with NGK technical support today about the discontinuation of the 23151 O2 sensor. They informed me that both the 23151 & 23506 were discontinued due to sensor failures and have been redesigned. The redesign is complete and they are set to be released next month under new part numbers. I plan to call back to get the updated part numbers sometime next month when my engine build is closer to being finished.

Old Man Minimalist

I believe the 23151 fits my '99 but not sure on the 23506. What years do these fit?

UKXJ

Of course, it may not be a Jeep application at all.

Saudade

Here's the NGK/NTK parts finder.

https://ngksparkplugs.com/en/part-finder

The ones OP quoted are the 2 upstreams for his 2001.

Old Man Minimalist

I like that part-finder you linked.

TheVet

Yes these are the upstream for 2001 4.0 as previously mentioned. The 23151 has become nearly impossible to locate online and locally. Not all models have different sensors for each bank like the 2000 & 2001 do. I used the NGK part finder listed above to see which ones mine required.

Graham123

Does anyone know whether or not the redesigned o2 sensors have been released yet?

TheVet

Then ngk parts finder website has not updated to show any different part numbers yet.

318SixPack

Looks like 23151 is the upstream sensor for 1997 and newer.

23121 is still the upstream for 1996 and older. Just replaced mine this weekend.
https://shop.advanceautoparts.com/p/ntk/20501668-P

Graham123

Okay I have an 01 XJ with the dual precats and 4 o2 sensors. From what I can tell both of the precat o2 sensors have been discontinued.. that’s for NTK part # 23151 and 23506 Iv been able to find the post cat o2 sensors but have had no luck finding the precat sensors. Iv ordered a set of Denso o2 sensors for the time being hopefully they work out okay but from what Iv read our jeeps are picky when it comes to anything but NTK o2 sensors.

cdurth

anyone have an update or any luck with alternative sensor?
I've been troubleshooting o2 issue now and replaced both upstream and downstream on my '00 last year (2022) with NTK replacements.
Just came across this mentioning that 23506 may have issues.
Finding it pretty difficult to find the specific part # of alternative brands for a federal emissions '00.

Graham123

I have an entire set of Denso O2 sensors but have yet to put them in so I can’t speak for the durability.. the part numbers for the denso o2 sensors are 2344076 (precat front), 2344077 (precat rear), 2344008 (postcat front) and 2344078 (postcat rear). You can also cross reference the NTK sensors on https://www.oxygensensor-crossrefere...vert/ntk/23110.

Graham123

im sorry I just reread your post and noticed you said federal emissions.. the part numbers I gave you are for cali emissions I’m not sure if the same sensors will work or not. You can still cross reference your Ntk sensors using that website I posted and it should tell you which sensors will work in all the different brands Bosch, DENSO, etc..

TheVet

I called and spoke with NTK/NGK customer service for an update. The person I spoke with today says that 23151 still says “inactive” with no update on anything being developed. And now the 23506 shows “obsolete”. He said he would not be hopeful about either of them getting replaced. Not sure where the other person I spoke to was getting their info. So I am not sure if they are going to produce replacements. Might have to start looking for an alternative source.

But I'm the captain

I just got off the phone with NTK to get an update on this situation and they said that both 23506 and 23099 (upstream and downstream non Cali) part numbers have been replaced by 23179. He said that it's a new part number and they made some modifications so that this one sensor will work as an upstream and downstream sensor. I can't seem to find them locally but placed an order from the ntk website directly. My current ones are still good but a little old and sluggish. I'll update once I get them installed