someone said theres only 2 o2s and i see four i see 2 under the engine and 2 above which on and if you could tell me which one is the upstream

 

The ones closest to the engine are upstream (sensor 1) the ones further down the exhaust are down stream or sensor 2.

As far as how many yours has, I think it depends on the year and the emissions regs are that time. Also if it is/was a California vehicle could have an effect on the emissions equipment.

 

If you have an XJ with just one O2 sensor it is threaded into your exhaust manifold (Renix) or into the "S" pipe just below where the pipe bolts to the manifold collector (91-95 HO). Based on what I know about rigs with 2 O2 sensors. You have an "Up Stream" which will be in the exhaust manifold or in the exhaust pipe just below the manifold. The other O2 sensor is called the "Down Stream" and it will be in the exhaust pipe somewhere near the inlet of your Cat. If you're looking at sensors anywhere else, they are not O2 sensors.

 

Second one should be behind the cat correct??

 

so when i change it i need to be on the ground?

 

yes auto zone has a special type of wrench kinda like a flare nut wrench used for taking out o2's if your try a regular wrench you have a 50/50 chance of rounding it.

 

at work we use a regular wrench and heat the threads around it cherry red and they usually come right out

 

:cough: 2000 has 4 o2 sensors :cough:

 

so how do i know which one

 

If the computer didn't tell you then replace them all.

There is a socket with a slit in one side that is made for O2 removal. I have two, one in my Jeep Toolbox and one in my shop toolbox. Heat usually helps to keep from breaking the bung out of the exhaust pipe or header..

 

X2 run the car around town for a while then slap on some gloves and GET ER DONE........
If you dont know when the last time they have been changed chances are good they are original. almost everyone over looks the replacement/funtion of a o2. They have a milage life spam. Dont wait for the computer to tell you they are faulty. Most shop manuals reccomend between 50-75K replacement. If your wallet can take it do them all. Use bosch!!

 

What size is the socket or is it just called an O2 socket?

 

theres 2 types of o2 sockets, ones more like a crowsfoot and the other is a socket with a slit down the side. yes they are called o2 sockets.