[pennybuy]

I bought a 97 Jeep Tj... on the way home the check engine light came on. I took it back and the dealer had his mechanic check it. He replaced the front (upstream) O2 sensor. Everything was fine. The next day the check engine light came back on...I did the code check on the dash...code 21 came up which indicates a O2 sensor problem...Now I see there are two O2 sensors...should I go ahead and replace the downstream (rear) sensor also ??? One site says something about 3 sensors...upstream..downstream and a left O2 sensor...so just how many O2 sensors are on a 97 Tj...

Thanks Bill

 

[1BLKJP]

I believe there are only two on that model. The one by the collector and the one just past the cat.

You should just have the dealer replace it also. But if you have to do it your self it is real easy to do.

 

[khenderson]

there's only two on my 97. like 1BLKJP said, there's one in the exhaust manifold and one just after the cat.

 

[pennybuy]

Thanks all...yeah I thought there were only two...that's why I couldn't understand what it was talking about when it said left side O2 sensor...I knew there was a front and rear one. The front one was changed so I guess I'll just change the rear one and see if that takes care of the check engine light.

Thanks again...Bill in Jacksonville Florida

 

[4Jeepn]

Most jeeps have 2, some have 4. My 2000 has 4 of them. why, because it has CA emissions on it. On our 97, it has just the normal 2.

 

[97tjcse]

o2 replacement

My two cents.
Left and right usually implies dual exhaust (not 4.0L). It has also been suggested that both o2s should be replaced at the same time for performance reasons and to head off the inevidable. I have a friend that replaced both and it increased his gas mileage 2 or 3 mpg's.

Good luck, sounds like you are on the right path.
97 owner and love it.

 

[Jerry Bransford]

As said, the '97 has two... an upstream and a downstream sensor. Only the upstream sensor affects mileage as it's the only one that is used by the computer to set the fuel mixture. The downstream sensor only checks the cat for proper operation.

Other than all that, yeah, I guess all you can do is replace the downstream sensor now.