O2 sensor advice

[sumtingwong]

Looking for some advice.....2002 tj 4.0, 135k miles. Has been running fine, started it this morning and running rough,chugging at idle,poor throttle response. I shut it off pulled codes using the odometer method. P0135,P0300,P0302,P0155. Have determined that these codes mean both upstream sensors have faulty heater circuits and other codes indicate cylinders misfiring. Please correct me if I’m wrong. What are the chances both sensors going bad at the same time? Have checked botn sensor heater circuits and each are Showing approx 6-7 ohms,is that a low reading? Best i can tell that is an acceptable reading, am i even on the right track? Possibly something else triggering O2 sensor codes? Any help is appreciated....sometimes really miss the carburetor days.

 

[Chris]

The chances of both O2 sensors going bad at the same time aren't that unusual.

However, don't be dumb. If you are replacing one O2 sensor, you should be replacing ALL of them.

Don't cheap out and be the guy who just replaces one. With as little as they cost, it's good preventative maintenance.

Your vehicle has 135k miles on it. Have the O2s sensors ever been done? If not, you're long overdue for them to be replaced. They should typically be replaced around 80k miles regardless of whether they are bad or not, as they are a normal wear and tear maintenance part.

My guess is that if you replace all of them, the codes will go away. If not, there's a chance it could be the pre-cats, but it's always the best bet to start with the O2 sensors, especially given your higher miles.

Last but not least, if you do replace them, read this thread:

The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread

Don't use anything but NGK / NTK sensors or you will have issues and your codes won't go away. That thread has information on why this is.

 

[sumtingwong]

Thanks,have read the thread. Wished i had found it sooner,good stuff! Hoping O2 sensor replacement is my fix. Starting the Kroil massage today, 4 sensors on the way. Thanks again

 

[Chris]

Happy to help! Let us know what ends up happening.

 

[sumtingwong]

Replaced all o2 sensors,started it ,chugging at exhaust,missing at idle. Haven’t driven much,not really very drivable with the missing scenerio. No codes yet.....if cats are bad are these the symptoms,will the trigger a code?

 

[AndyG]

Replaced all o2 sensors,started it ,chugging at exhaust,missing at idle. Haven’t driven much,not really very drivable with the missing scenerio. No codes yet.....if cats are bad are these the symptoms,will the trigger a code?

Put your hand over the exhaust and see if it’s got good flow , sounds like you have clogged cat

 

[Quigley]

Front pipe. Just in case.

I had to replace mine this past winter. I ended up replacing the cat and went with a banks monster exhaust since it all had to come down and was 18 years old. I was able to get everything for $750, but I had to shop around.

The job wasn’t that bad if you need to go this route. You need a swivel socket to really get the pipe to manifold bolts. I sprayed everything with pb blaster several times before I started. A second set of hands helps when going to install the front pipe.

 

[sumtingwong]

Thinkin i may have to do the same...how did you determine that your cats were bad? Never had a bad cat on any vehicle i have owned,so wouldn’t know a good one from a bad one. Trying to diagnose my problem before throwing parts at it,trying to change my ways

 

[sumtingwong]

Flow seems strong....still no codes...

 

[Quigley]

I replaced all 4 of my o2 sensors and I was still reading codes for the o2 sensors. I came across a post that mentioned that it can be the precats that fall apart inside. It went away after replacing the front pipe. I was also getting a code for a CPS and the Camshaft sensor along with my o2 sensors. So I ended up replacing everything at once. Mopar for sensors and NTK for o2.

Have you changed your plugs recently? App985 auto lites work well and are cheap. Try cleaning the throttle body and IAC sensor both are free to do and then you can rule those items out. Mine drove like shit for weeks before the codes started showing up. The o2 are wear items and can be transferred to the new pipe if needed.