There are two O2 sensors on an XJ.

One is just behind the header, in front of the catalytic converter. That's the one that most often will affect gas mileage. If your sensor's been in there for 100,000 miles or more, it's not a bad idea to replace it "just because".

The second one is behind the catalytic converter, and sniffs the exhaust to make sure the converter is doing its job. Not as likely to cause a problem with gas mileage, though it can affect it.

They're not that hard to change - just make sure you get the right one (there are a host of different options, including getting a cheaper generic sensor and wiring it to the old plug). The big issue is usually rust (they've been living a very tough life, so don't always like to come out). They make special slotted sockets for working around the wires, but I've always just used a wrench to honk on 'em.

 

There are two O2 sensors on a 2001 XJ.

...a RENIX only has one.

Follow the exhaust pipe...and yes...you have to get underneath the Jeep to see it.

 

Yes.

Not too bad. Just un-clip them from the harness and unscrew them from the exhaust. If they are as tight as mine were, you will need a pipe wrench and the end of a jack handle to get them out. I also had to use an 18mm 02 thread chaser.

Probably not unless they are bad.

 

but I've always just used a wrench to honk on 'em.

Do you know the size? I attempted mine and didn't have the right size.

 

I don't recall off-hand (I'd guess 19mm). Heck, I might have used a pipe wrench (on the old one, that is...), though I don't recall having any problems getting them out. OTOH, that IS one of the big advantages to living in the desert - it's a lot easier to remove parts. ;-)

 

I think it's a 22MM, but I'm not crawling under the truck to check.

 

If your mpg's are below average by 30-40% you may need new O2 sensors. The typical service life of an O2 sensor is about 100-150,000 miles.

A 2001 XJ Cherokee should have 4 O2 sensors, like in the picture. 2000 can have 2 or 4 O2 sensors. 1996-1999 have 2 O2 sensors.


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CJ7-Tim is correct... 2001 has 4, 2000 can have 2 or 4, most other years have 2.

There is a special wrench you can buy to remove O2 sensors so you dont mess them up. I soaked mine in PB Blaster for a few days, came right out with the O2 wrench. I picked up about 10% better mileage too.

 

I have a 2000 xj 4.0 and it has two sensors but the one that is supposed to go behind the cat is in front of the cat instead of being behind it..why would this be?

 

....why would this be?

Maybe some dipstick installed the cat backwards ?

 

Seen deer whistles installed backwards.... attracted deer!!! Yikes!!

 

Ha ha... or maybe they make a sucking sound?

If the rear O2 sensor is installed before the cat, I bet your Jeep is not running as well as it should? The 2nd O2 sensor measures Cat performance, and will be reporting pretty bad stats if it is before the Cat.

Again, Tim nailed it... sounds like someone installed it cat-backwards?

:shhh: oops

 

Idk why but was in front of the at but I took to all off and swapped it around so it's right now

 

Yea I pulled it off and flip everything to where it was right..but now I'm having some problems with my cps I think poped a u joint earlier today and my gf zj poped a freeze plug so it's been a great day for me

 

Any one by chance know the NTK part numbers for the O2 sensors?

2000 cherokee I-6, it is equipped with 4 sensors. 2 up top, 2 below

 

Hi All, got the dreaded check engine light and the code point twords the catalytic converter/02 sensors (x 2)and I am just going to replace all. Does anyone know the best manufacturer and part# for the catalytic converter and O2 sensors for a 98 jeep grand cherokee 4.0?

 

pic of the sensors and part numbers.

 

pic of the sensors and part numbers.

Thanks Ken it's appreciated mucho but here is a couple shots of my exhaust, note that mine is a single exhaust from the header on back to the converter (pipe at converter is dbl bolted on) and then at the muffler it's welded on. I was going to do this myself but it looks as though I would have to weld the new cat on to where it connects at the muffler and I simply don't have a lift nor access at this time to a oxy/acc weld rig.

 

 

My 2000 XJ has 4 sensors. I read my code and it was a P0135 1/1 O2 sensor heater. I determined that 1/1 means it's the one towards the top of the engine towards the front for the first 3 cylinders. If you look at the picture in a post above by CJ7-Tim you will see this detail. I bought the special wrench for $30 and an O2 sensor from pep boys for $67. Once I got under there I thought I was never coming out. That sucker is way up in there. Very hard to get leverage. It doesn't help if you're turning that bugger the wrong way either which is easy to do because it's hard to get up in there. Once I started turning counterclockwise she came right out. New one went right in. On to my next code!