[PMAZ7]

I just got a check engine light, I've had the Jeep for 4 days now. No big deal. I checked the codes and it flashed the obvious 12, then 21, then the ending 55. It says check/replace oxygen sensor. Is there anyway to clean the O2 sensor? What should I look for around the sensor that could have thrown this code? Dirt? Worn wires? Thanks for your help in advance.

[Matt Gertsch]

The heating element could have burnt out, or the electroplating could have burnt off of the sensor.

[PMAZ7]

Do I have two O2 sensors or one? Also, there are so many different part numbers, what am I looking for to replace it? Thanks. Also, is this a huge MPG issue? What else does it effect? Cat?

[fitbmxseries1]

you have to just replace it no way around it, theres an upstream and a downstream 02 sensor. unfortunatly the downstream one cost 120$ and the up stream one is 90$... maybe find a good deal online though? id say go to an avanced auto and buy a bocshe one . ive never replaced an upstream on a car its always been the downstream one... probably why they cost so much. Did you use the diagnostic that just flashes then you decifer the code? or was an an actual diagnostic computer? if it was a computer it should say o2 sensor #1 or o2 sensor #2 ( 1 being the upstream and 2 being the downstream) and im sure you could go to any advanced auto or auto zone and they would use the code reader and point you to the correct sensor. hopfully that helps. and good luck

[PMAZ7]

Thanks, that's a huge help.

[Mee_Too]

I just went through this last week. The "Check Engine" light came on a couple of weeks ago, and the trouble code I got was P0138, which was the rear O2 sensor (between the catalytic converter and the muffler).

It was pretty easy to replace...didn't have to raise the Jeep at all, just placed a carpet mat under it and scooted under. There was a four-conductor wiring harness about a foot long running from the sensor to a connector. The connector was kind of protected by a plastic cover held to the underside of the Jeep by a single bolt.

The new sensor came with some anti-seize compound already applied to the threads.

I got a "universal" O2 sensor from a guy on eBay for $21.49 + $5.00 shipping. It came without the connector on the end, I cut the connector end from the old sensor and spliced it onto the replacement sensor. Also, this same "universal" sensor is supposed to work as a replacement for the front sensor, too (apparently, the only difference between the front & rear sensors is the connector), so I ordered an extra while I was at it.

The brand of the new sensor is NGK ( I guess the spark plug company). So far, so good -- I erased the code, and the MIL has stayed off.

I've never used an NGK product before -- I guess that time will tell how it holds up...

[PMAZ7]

I'm not so good with the electrical end of things, so I'm wondering how much the non-universal (one with the connector) would be. Also, what is the MIL (I'm completely new to the Jeep thing). Do I reset it by disconnecting the battery? Or will it just reset itself? You guys are so great with the help!

[Mee_Too]

MIL = Malfunction Indicator Lamp = fancy word for "Check Engine" light. (I read "MIL" so many times while reading about sensor replacement, that I started using the expression without meaning to )...

Anyhow, I'm not sure if disconnecting the battery will remove the code...I used a code scanning tool...maybe someone else will chime in about the battery disconnecting.

As fitbmxseries1 mentioned, parts stores will hook up a code reading tool, and tell you for sure what code you're getting, so that you replace only the necessary part.

If it does turn out to be your O2 sensor, here's a link to Advance Auto Parts' selection of sensors (I'm not necessarily endorsing Advance):

http://www.partsamerica.com/ProductList.aspx?parttype=291&ptset=A&searchfor=Ox ygen+Sensor

I saw a Bosch rear sensor #13138 with connector on eBay for $47.57 + shipping, so they are available there, too.

[PMAZ7]

Man, I really appreciate the part #'s too! You guys are making it easy, and I appreciate it. If I can help with anything, just let me know.

[Mee_Too]

Hey, no prob...

I'm new to the Jeep world myself, picked up a '99 XJ Sport a little over a month ago. This oxygen sensor thing is the first thing I've tackled on mine. I enjoy reading all of the posts here, and am impressed with the knowledge these guys here have!

I changed the ZIP code at the Advance Auto Parts page to a random one in AZ, since I see that's where you are (I'm in IL)...if I'm not mistaken, the prices come up differently (lower)! In-store prices might be different yet...

As mentioned, you should have one of the parts stores check codes for you, so you don't end up replacing parts unnecessarily.

[PMAZ7]

I have a good friend that has been my race mechanic for some years, over the years. He definitely knows his stuff and has all the scan tools you could imagine. I'll use him. Matter of face he told me something about "something wasn't warming up on the O2" or something like that... I don't know much about cars/trucks... I just race them!

[Mee_Too]

Your mechanic friend should be able to determine the code for you...good luck!