Hey everybody. I'm new to the forum. I've had my Wrangler for a couple years but just got my first Cherokee XJ in December.
Among other issues, it's giving me codes "P0171" and "P0133," which I understand means I should check or replace the O2 sensor. I looked on Autozone's website, and they have an up-stream sensor (located before cat converter) or a down-stream sensor (located after cat. How can I tell which one I need? (Other than buying one then buying the other when that doesn't fix it. Lol)
It's a 1999 Cherokee 6.0
Thanks in advance!

 

my obd2 "actron" scanner showed me which one was inactive

 

As did theirs, bank one, sensor one...check the upstream sensor. It's the one just off the exhaust manifold. Check the wiring.

The P0171 says it's running lean, P0133 is sensor circuit slow response...

If the wiring looks/tests okay, check for exhaust leaks...most common spot is at the collector/s on the exhaust manifold. If that checks out, get a new sensor.

 

NTK brand oxygen sensors work best. That is what the factory used.

NTK 23151 (upstream - before the cat)
NTK 23099 (downstream - after the cat)

http://www.rockauto.com/en/catalog/j...2)+sensor,5132

 

Welcome to CF Katie! X2 on this...

X2 on this as well. Though the OEM NTK/NGK's will cost a premium they are truly one of those items where you get what you pay for. I recommend sparing yourself the headache.

 

Before you go at the O2 sensor with a wrench, do yourself a favor and hit it with PB Blaster or Kroil and let it soak before trying to get it out. It's also easier to remove if you run the engine long enough to get the exhaust up to running temp, but be careful not to burn yourself if you do that.

 

Solid info in this thread

1. Definately check the wiring to make sure nothing is melted

2. PB Blaster for a few days, best to soak when the exhaust is hot

3. Use the exact sized wrench for the job, or use an O2 sensor socket. The exhaust rusts very easily and the factory O2 sensors did not use any anti-sieze

4. Get the exhaust as hot as you can before trying to turn it with a wrench. I almost stripped my front socket removing it while everything was cold. Went for a 20 minute ride and it came apart super easily

5. Only use NTK sensors, check eBay and Amazon for the best price. I found mine open-box on eBay for $20 each, got really lucky
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Can't emphasize that enough. No amount of PB Blaster is going to help you on a cold exhaust.

Also, do NOT try to remove one of these with an open-end wrench (see below). You must use a good quality socket, and it's better if you use a 6 point socket (not the more common 12 point socket), and best if you use the special socket that's made for these.




6 point socket (on left) vs. 12 point socket (on right)



Open-end wrench


O2 sensor socket (typical. There are variations.)

 

all of the above.

I did the upstream sensor on my '98, and it seemed no amount of grunting and cursing could get it out. I heated the bung on the exhaust with my propane torch and it still wouldnt budge.

So i run down to the neighbor's who as a "good" torch, and an actual O2 sensor socket like shown above. then it came out easily.

runs a whole lot better. How is yours running? Mine would fall on its face shortly after you start it up, but after it stumbles around trying to kill itself, it ran normally.