The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread

[JpZombie]

Once my 2004 LJ warms up the idle starts surging/pulsing. If I rev the engine up it is smooth with no stumbles, but once I take my foot off the gas it will drop back down to idle and kill the engine sometimes. No codes being thrown. I cleaned up the IAC sensor, which didn't look bad, but was still going to clean the housing out as well. No change after cleaning the IAC.

Can this be O2 sensor related? When checking with the code reader I get B1-S1 throwing numbers all over, B1-S2 holds steady around 0.80vs, B2-S1 numbers all over, and B2-S2 holding steady around 0.80v. Should I be looking at replacing the O2 sensors?

 

[reddvltj]

Once my 2004 LJ warms up the idle starts surging/pulsing. If I rev the engine up it is smooth with no stumbles, but once I take my foot off the gas it will drop back down to idle and kill the engine sometimes. No codes being thrown. I cleaned up the IAC sensor, which didn't look bad, but was still going to clean the housing out as well. No change after cleaning the IAC.

Can this be O2 sensor related? When checking with the code reader I get B1-S1 throwing numbers all over, B1-S2 holds steady around 0.80vs, B2-S1 numbers all over, and B2-S2 holding steady around 0.80v. Should I be looking at replacing the O2 sensors?

B-1 is going to bounce like that. The ECM uses data off of B-1 to adjust fuel trim. B-2 is strictly a cat monitor. If it were bouncing it would likely throw a code.

I would check the voltage on your TPS.

 

[Statler Waldorf]

First post!

I bought an '01 TJ Sport with a 4.0L 6cyl in late '24 and have been doing lots of small things to get it fixed up. But I'm not sure how to proceed with the CEL for the O2 sensor (sensor 2 bank 2.)

The mileage is 200k, but I've been told that the engine was rebuilt at 130k (which may or may not be true.) Mechanically, it's stock.

The previous owner replaced the O2 sensor, but it did not fix the CEL. I've cleared the code a couple of times, and the CEL comes back. Once in about a day. Once in a couple of hours. Here's the sensor he put in...

I assume the relay is good, otherwise both bank 2 sensors would throw a code. Correct?
I have no idea how old the CATCO is, but to look at it you wouldn't guess it's 200k miles old.

I don't want to throw money at parts without some probability that it will fix things.
Is there a way to test the O2 sensor?
Should I replace the relay even though I think it's okay?

Thanks for your consideration.

 

[AWayne]

First post!

I bought an '01 TJ Sport with a 4.0L 6cyl in late '24 and have been doing lots of small things to get it fixed up. But I'm not sure how to proceed with the CEL for the O2 sensor (sensor 2 bank 2.)

The mileage is 200k, but I've been told that the engine was rebuilt at 130k (which may or may not be true.) Mechanically, it's stock.

The previous owner replaced the O2 sensor, but it did not fix the CEL. I've cleared the code a couple of times, and the CEL comes back. Once in about a day. Once in a couple of hours. Here's the sensor he put in...
View attachment 584751

I assume the relay is good, otherwise both bank 2 sensors would throw a code. Correct?
I have no idea how old the CATCO is, but to look at it you wouldn't guess it's 200k miles old.

I don't want to throw money at parts without some probability that it will fix things.
Is there a way to test the O2 sensor?
Should I replace the relay even though I think it's okay?

Thanks for your consideration.

Do you have access to an OBD2 code reader? One with "live data" functions?

If you do, start the jeep and let it run. Your oxygen sensor should read between 0.1 volt, and 1.1 volt on the live data function. If it does not, try a new one.

I have not had much luck with NTK oxygen sensors. Walker oxygen sensors have worked better for me and my friends with 4.0 Jeeps.

https://www.ngk.com.au/technical_in...xygen sensor,should be about 300 milliseconds.

 

[Statler Waldorf]

I use BlueDriver. It does support live data.

I'll check that out tonight and let you know.

Thanks.

 

[jim_lukens]

I have and 01 sport manual 6cyl 4L. I had to purchase a couple times until I got an ngk one that worked right and kept the codes cleared after I installed and cleared them. Not sure about quality control on those things. But it cleared. However I eventually ended up replacing the precats as that was really what was causing the issue. I have 180k and the originals lasted that long.

Did the o2 sensors myself but the cats are a big job so I went to a shop ran about 1200.

Best of luck. Good thing is that's it's drivable and I drove for the better part of a year w the codes on and Jeeps running fine. But it's nice to have the codes gone though

 

[jcw]

You'll definitely need to get a proper code to diagnose. I had multiple issues and was able to one by one clear the issues with the proper codes and diagnostic approach to each one. Hopefully you only have one code. It can be incredibly frustrating but may be something simple. Post back your obdii results

 

[Statler Waldorf]

I should have included the code in the original post. Sorry for the oversight.

P0161 O2 Sensor 2/2 Heater Performance

That's the only code.

 

[jcw]

I had that code with a new o2 sensor. Turned out to be a wiring issue. Make sure the plug is fully seated on the sensor to wiring harness. Inspect all pins for any damage/loosness. Then check the plug that goes to the engine wiring harness. Mine had a loose pin that wasn't making contact. Once fixed, light went away almost immediately. Plus gas milage was improved dramatically

 

[Statler Waldorf]

I had that code with a new o2 sensor. Turned out to be a wiring issue. Make sure the plug is fully seated on the sensor to wiring harness. Inspect all pins for any damage/loosness. Then check the plug that goes to the engine wiring harness. Mine had a loose pin that wasn't making contact. Once fixed, light went away almost immediately. Plus gas milage was improved dramatically

That's a good tip. I'll definitely check that out. But not tonight (too cold and dark.)

Thanks.

 

[JoseA]

I should have included the code in the original post. Sorry for the oversight.

P0161 O2 Sensor 2/2 Heater Performance

That's the only code.

I had this code once. I "reset" the computer by unplugging the negative cable from battery for a while. then I checked the bolts to the exhaust precats and they had gotten loose. after I tighten those up the CEL did not come back.

 

[Statler Waldorf]

Connected up my BlueDriver last night and, at idle, the voltage ranged between 0.32 and 0.38. When I revved the engine, it jumped to about 0.85.

The tool didn't explicitly present the latency between signals, but they did not seem slow.

Any idea what that means?

Thanks.

Edit: And I now have a second (unrelated?) code. P0456 Evap System Small Leak

 

[macleanflood]

Connected up my BlueDriver last night and, at idle, the voltage ranged between 0.32 and 0.38. When I revved the engine, it jumped to about 0.85.

The tool didn't explicitly present the latency between signals, but they did not seem slow.

Any idea what that means?

Thanks.

Edit: And I now have a second (unrelated?) code. P0456 Evap System Small Leak

Generally speaking under .9v is a good O2. That's one of them...my 97 has two...the newer ones have 4.

Evap system could be as simple as a loose or old gas cap. Smoke test usually reveals everything.

-Mac

 

[AWayne]

I should have included the code in the original post. Sorry for the oversight.

P0161 O2 Sensor 2/2 Heater Performance

That's the only code.

Check the ground on the block. Big ole stud with a ground strap can't miss it. Also check the fuse for the Oxygen Sensor(s). The heater circuit is fused.

Connected up my BlueDriver last night and, at idle, the voltage ranged between 0.32 and 0.38. When I revved the engine, it jumped to about 0.85.

The tool didn't explicitly present the latency between signals, but they did not seem slow.

Any idea what that means?

Thanks.

Edit: And I now have a second (unrelated?) code. P0456 Evap System Small Leak

From my understanding, lower voltage (0.5 and below) corresponds to a lean condition.

High voltage (0.5 and higher) is a rich condition.

While 0.38 is within spec, it would indicate a slightly lean condition. Might be a small vacuum or seal leak. Or a gas cap or something.

If you have an evap code, start checking the lines the run to evap box and whatnot. Look up some diagrams in the FSM.