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Downstream or Catalytic Convertor O2 Sensor

heyhar

NAXJA Forum User
I'm replacing the cat and the rest of the exhaust system in my '96. It's been rattling for a while, but now it's broken and leaking, and throwing a code. I've got a new Walker cat, but before I tear the exhuast system apart, I need to order a new O2 sensor to install into it. Looking at a few vendor's websites, there seems to be no consensus as to what I need. Two or four wires, heated, I just don't know. I won't be able to look at it till tomorrow, and I was hoping to order it tonight. Any thoughts? Thanks!
 
'96 was a change over year so you might not be able know without looking at it. I don't know if the changes affected the O2 sensor so maybe someone with more knowledge can answer.
 
Um, go to your choice of parts store web sites or rockauto, plug in your vehicle info and it will give you a PN that fits your vehicle.
 
Johnnie, I had Rock open on one screen, Summit on the other. Each had a variety of choices. I'm figuring that the rear one is rather generic, but the text describing them is confusing. I guess it's tough to write a sexy description for an O2 sensor, but I wouldn't mind some facts. Now I gotta go outside, in single digits, crawl under the car in snow, and see if I can figure out what I need!
 
Your 96 may be different than mine, mine is an export model. I've tried numerous times to find the proper rear O2 sensor and never succeeded. The problem is the connector, it never matches what the book calls for.

I finally chopped the wires on a new O2 sensor (wrong connector) and used the old connector. I just matched the wire colors and used crimp connectors. It is recommended not to solder.

The number I tried was Jeep 5604 1005. But I was trying to use an aftermarket sensor cross referencing the Jeep numbers and never did get an exact match in the physical world. You might try this number and have better luck than I did. My 96 is odd in many ways.
 
I just bit the bullet and went to the local NAPA store. I was asked about the length of the wires, which I didn't know, so I asked for the longer one. I had the same problem with the front, and ended up with a coil of extra, 'cause I needed the short. I paid double buying it locally, figuring I could return it if it's wrong, rather that sitting for weeks waiting for another. My '96 is an earlier one, so I'm hoping it's right. My son has a very late '96, the 'Classic' model, which, electrically, is mostly '97, underneath and under the hood, and it's a real pain to obtain some parts for. His was made well after the change-over to the '97 would have occured, as they were trying to use up the remaining old parts.

I took my '96 in to a dealer for the recall back in 2010, to check the cat and re-flash the computer. A week later the cat was rattling, and a series of events started which led to me replacing the TPS five times over the next year. In the last few weeks, the innards in the cat have completely broken, and it sounds horrible, and threw a code for the rear O2 sensor, which will not clear. I have a new Walker cat, and a new Walkes Dyna Max cat-back exhaust, but with the crappy weather, I'm hoping to do it all in one day in the garage, if I can get all the slop under the Jeep to clear off. It couldn't have happened in June.....
 
I hope your plug matches up for you. My local parts supplier told me the long wire O2 sensor is for the ZJ? My 96 has a mix of 95/96 connectors, mostly in the passengers side motor harness. My local parts place is about 20 miles. I tried to do it over the phone using overnight UPS, which failed twice. As long as the connector matches you should be OK. An M10 (pretty sure maybe a M12) nut fit the threads for the wire hanger on mine fine, after I destroyed the (cheap) factory nut trying to get it off of there.

I'll never try another CAT, muffler or tail piece without a torch. I ran out of oxygen and tried doing it cold last time, what a pain. Remember the exhaust in connected to the exhaust manifold, BFH's and/or lots of muscle are a no no.

Be sure and check your O2 heater fuse, just in case.

I've been holding off doing a bunch of stuff hoping for some warmer weather, I have inspection and smog this month.
 
I don't have a 96, but RockAuto has 2 classifications: upstream and downstream. Basically 2 sensors for every brand, plus a couple of odd ones for export or whatever. I bought NTK for my junk, and they shipped me the correct sensors.

NTK Part # 23121 NTK OE Type
Upstream; NTK is Original Equipment

NTK Part # 23014 NTK OE Type
Downstream; NTK is Original Equipment
 
Sometimes they make an extension pigtail, plug into the sensor with another plug on the other end, for another 18" of pigtail.

The Upstream O2 sensor is for the feedback to the PCM on the A/F ratio. The downstream O2 sensor behind the CAT is just to meet the OBDII requirement of running a self-test on the CAT to make sure it is working properly. What the PCM does to perform the test on the CAT (and it only does it occasionally, NOT constantly) is to compare the outputs of the two O2 sensors. If the outputs are the same, the CAT must NOT be doing its job of combining chemicals in the exhaust to breakdown the pollution, which would consume some of the oxygen in the exhaust, if the outputs differ, then the CAT must be working.

So logically, it would be wise to get the same brand of O2 sensors, in case they differ in their output slightly from manufacturer to manufacturer (and they do sometimes), but honestly its NOT likely to be a problem.

Like mentioned already, the only difference is the length of the pigtail for the wiring. On most vehicles they have the same connector, I don't know for a fact the connector is the same on the Jeep XJ. My XJ is '95, before the 2nd O2 sensor was mandated by OBDII in '96.

And if you didn't know already, the upstream O2 sensor is important to the proper operation of the motor and will effect mileage, even power and clean running of the motor. It is being checked constantly when the PCM is in closed loop (most of the time). The downstream O2 sensor is just to check the CAT is working.
 
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