O2 Sensor Swap Walk-Through

fuse

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I had a CEL with a P2098: Post Catalyst Fuel Trim System Too Lean Bank 2 code recently. Since I suspect my O2 sensors are more than 15 years old, I figured swapping them would be the first fix I'd try.

This walk-through is for the 4.0L I6 with California emissions. The 4.0L engine with Federal emissions and the 2.4L engine only have two O2 sensors in different locations than my engine, but the general process is the same.

Step 1: Get the tools and parts.

You want an O2 sensor socket and a tap to chase the threads. I used these tools, but there are other options just like them:

https://www.amazon.com/gp/product/B00GMN4D1Q/?tag=wranglerorg-20

https://www.amazon.com/gp/product/B000XETMW0/?tag=wranglerorg-20

You might as well do all the sensors at once. The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread has all the right part numbers for the NGK/NTK sensors you need.

Step 2; Find all the O2 sensors and plugs.

The FSM diagrams are only so good and they don't show where the plugs are. Fortunately, the wiring harnesses are short. Unfortunately, one of the plugs is hard to get to. Here's where the O2 sensors are:

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The 1/1 and 2/1 plugs are on the plastic rail that runs along the intake manifold, with 1/1 at the front and 2/1 at the rear.

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The 1/2 plug is below the driver's side motor mount. And the 2/2 plug is mounted right on top of the forward end of the transmission — which makes it really hard to reach.

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Step 3: Remove an old O2 sensor.

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I was fortunate that the old sensors weren't too stuck, but soaking them with penetrating oil beforehand can help.

Unhooking the plugs takes two hands, one to release the catch and another to pull the plug apart. The only plug that's tricky is the 2/2 plug on top of the transmission. If you get right under the Jeep, you can snake one hand up next to the Bank 2 cat to release the catch and get another hand up over the transmission to pull the plug.

IMG_20210105_154954.jpg


I'm using a glove in this picture, but I recommend doing this with bare hands so you can tell what you're working with.

Step 4: Chase the threads.

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It's easier to do this with a box end wrench so you can work the tool back and forth without having the wrench slip off.

Step 5: Install a new O2 sensor.

Make sure you have the right O2 sensor for the position it's being installed in. The plugs are keyed, so you can compare the old and new plugs. Also check to make sure the harness is the right length.

The instructions in the NGK/NTK box say to hand tighten then add 1/2 turn with the wrench. FSM says tighten to 22 ft. lbs., which is probably about the same.

I know some people suggest adding anti-seize to the O2 sensor threads, but both the FSM and NGK/NTK instructions advise against this. The O2 sensors should already have anti-seize already on them from the factory.

Step 6: Plug the O2 sensor in.

If you put a sensor in the wrong place, the keyed plug won't go in. Otherwise the plug just snaps into place.

Finish: Make sure everything works.

If you haven't done so already, clear any remaining fault codes from the PCM so the CEL goes off. If you have an OBD-II reader and app, plug it in and pull up the O2 sensor diagnostics. Start up the engine and check to make sure that the CEL stays off and there are no new faults. Watch the O2 sensor readings while the engine idles until the sensors warm up and start providing good data. The reported O2 sensor voltage should range between 0 and 1 Volts.
 
Excellent write up and pictures. I changed my 02 sensors and precats last month. I'm glad you showed pictures of where the plugs re for the O2 sensors. You're right, the manuals don't show you. I would like to stress that with my 05, there are 4 different O2 sensors, so making sure you've installed the right one in the right port is very important.
 
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@fuse , this is great; thank you. Curious if you saw any engine performance or MPG changes before/after?
I haven't seen the CEL since I did the swap, which was why I did it. That and preventative maintenance.

I didn't expect any performance or mileage improvements and haven't seen any. But I wasn't having problems with engine performance before the swap. I do check MPG occasionally, and did check it after the new O2 sensors went in but it's unchanged.
 
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I haven't seen the CEL since I did the swap, which was why I did it. That and preventative maintenance.

I didn't expect any performance or mileage improvements and haven't seen any. But I wasn't having problems with engine performance before the swap. I do check MPG occasionally, and did check it after the new O2 sensors went in but it's unchanged.
Thanks, I have the sensors ready to install but am not seeing any issues or MPG problems (~19MPG) and was curious.

One thing that I'd suggest is to reset the PCM after replacing these (or any other sensor that affects timing, fuel/air mix, etc) so it can learn from the new data.
 
Removing the plug on the 2/2 sensor is a PITA. Is there a trick to it? I have a stock 06, slid under the jeep with a creeper and don't seem to snake both my hands to unplug the connector
 
Removing the plug on the 2/2 sensor is a PITA. Is there a trick to it? I have a stock 06, slid under the jeep with a creeper and don't seem to snake both my hands to unplug the connector
Yeah, that one is a pain. Do it with bare hands so you can tell what you're doing. And if you get in just the right spot with your feet toward the passenger side you can get one hand up next to the Bank 2 cat and another hand up over the transmission. That way you can release the catch with one hand and pull the plug with the other hand.
 
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Yup, no fun. All I can say is to keep at it. I had one hand coming in from a different passage than the other.
 
Approaching the beast with the feet on the passenger side was the the turning point. Thank you for that tip @fuse .

Also, after replacing all 4 sensors and cranking the jeep I noticed fumes discharging from the Bank2 Sensor1(upstream). Is that normal or the sensor needs more tightening? I did a finger tight and then half a turn.
 
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Also, after replacing all 4 sensors and cranking the jeep I noticed fumes discharging from the Bank2 Sensor1(upstream). Is that normal or the sensor needs more tightening? I did a finger tight and then half a turn.
I don't think that's supposed to leak. Did you chase the threads before installing the new sensor?
 
I chased the threads. It seems to be some extra anti-seize which was smeared on the sides of the O2 sensor which is burning due to the high temperature. All good!
 
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