Sizemic2

I've learned that if it ain't broke, don't fix it. I have a 2001 XJ with the 4 O2 sensors and 2 pre cats, California version.

Changed all 4 sensors yesterday with the appropriate NTK parts. Today it throws the code, P0432 Main Catalyst Efficiency Below Threshold Bank 2.
Why would it be throwing this code? Runs fine. No code before new sensors, i replaced them because they had 125k miles on them and I was trying to be proactive. I also replaced the CPS with a mopar part. I drove around yesterday after installing the sensors with no code.

Any reason why a new O2 sensor could cause this the next day? I don't want to replace cats if i don't need to.

Sizemic2

Oh and i added some Lucas oil fuel system treatment last time i filled up, which was yesterday after replacing the sensors. Could this cause a CEL?

fb97xj1

Check the wiring and the exhaust for any leaks, and that the sensors are not loose. A bad cat is high on the list from what i have read for that code. The old sensors may have been compensating for it and the new sensors picked up on it. I have no clue with the oil fuel treatment. Never used the stuff.

Ralph77

Same exact problem with an '00. Replaced all 4 O2 sensors, figured they were original, had 150K on them, and needed to go. Then the P0432 reared its ugly head. First thought was that since everything is running more properly the new sensors picked up on it like fb97xj1 said. Also that it is most likely the cat like he said too. Thing is there are other things that could be causing it too. Vacuum and exhaust leaks. Fuel trims. Defective O2 sensors. Would not be the first time a new part was defective out of the box. Best I can tell is that my fuel trims are within reason. O2 sensors appear to be OK. Did find that I had a couple minor vacuum leaks. The front two hoses on the intake manifold. Fixed that code came back. Noticed that one of my rear exhaust manifold bolts was backed out a 1/4" so I retourqed all those best I could. Code came back. Noticed that my vacuum MAP ("HG) # looked a little funny on the freeze frame info for the P0432 so I replace the MAP sensor elbow. Waiting for the code to come back. Funny thing is the more I fix hoping it is not the cat the longer it takes for the code to come back. When the code comes back after the MAP elbow fix, I truly expect it to, I will either put back in the old rear downstream O2 sensor or defect it and try another one to see what happens. I am wondering if I managed to crack an exhaust manifold when yanking out the O2 sensors. Also I am wondering about the intake/exhaust manifold gasket. Problem with the last two is if you go through all the trouble to take off the exhaust manifold to inspect them and throw on a new gasket you might as well replace the cat while everything is apart. So that is where I am at and what I am thinking. Will post as things develop. Maybe you can do the same?

Sizemic2

Thanks for replies! Ralph, i do have a bit of a stumbling idle, always have, but i don't know how much of that is vacuum leak or just old inline engine technology. I replaced tps, iac, and cleaned the TB a few weeks ago and the idle was exactly the same, but no codes. That MAP tube did look pretty rough, but it didn't appear to be cracked. I'll have a closer look at the manifold bolts & gasket. I may throw in the old downstream O2 sensor as well, just to isolate the issue.

The CEL didn't come on right away, it came on when i accelerated quickly from a stop at a red light about 10 minutes from my house. And i drove it quite a while the day before after changing the sensors. An exhaust or vacuum leak would have been there the whole time, so it just seems like odd timing. I'll post updates on the situation.

madmanmarty

This is a great lesson for everyone.
Don't replace parts(except for maintenance items) unless you are getting codes,or something isn't running right.

robertj

O2 sensors are maintenance items:

http://www.autotap.com/techlibrary/r...aintenance.asp

The OP either got a bad one out of the box or fixing them showed an issue that may have been masked by tired O2 sensors.

Ralph77

To Sizemic2: The timing was odd on mine too. That is why I am trying to determine if it really is the cat.

To madmanmarty: I agree. Like the old saying in the army. "If it works don't fix it". But like robertj points out they kinda are. And I was hoping to improve gas mileage, really like my Jeep, and plan on keeping it forever. LOL

Jeep Driver

I keep reading this........over and over.........you and others keep doing this..........same questions.........


Turn off CEL and see if it returns.

extrashaky

If it does come to a cat replacement, the cheapest bolt-in is about $190 at CarID:

Walker 52304

CarID also sells that unit on Ebay for the same price. Everywhere else sells it for considerably higher.

Or you could get some small cats, cut the old ones out and weld the new ones in.

CCKen

The PCM gets a little funny when changes are made that upsets its predetermined set points. Introducing new O2S' may have given it fits - for awhile.


Do like Jeep Driver suggests and clear the code and drive it. Take it out on a freeway run to clear its throat.

Sizemic2

Erased code, drove around for an hour or so, no light! We'll see how long that lasts...

Sizemic2

Lasted a day.

I'm going to burn all this lucas fuel treatment out, reset the light and try again on fresh gas

CCKen

See if you can pull an O2S and see if there's any white deposit on it. Fuel additives and coolant will leave these deposits.

Ralph77

In the beginning right after I changed out all four O2 sensors the P0432 code came on pretty quick. I cleared it a few times, both by reflashing the computer (pulling and grounding the battery cable and doing the headlight switch thing) and just clearing it with my scanner. It would come back pretty quick. The more I fixed, the vacuum leaks and re-torquing exhaust manifold bolts etc, the longer it would take to come back. All this makes me wonder about CCKen's statement: The PCM gets a little funny when changes are made that upsets its predetermined set points. Introducing new O2S' may have given it fits - for awhile. Hey I have no problem replacing the cat if that is the problem. Of course I would rather not spend the money but whatever. My issue is that I am not 100% convinced it is the cat and if I replace it and it does not fix the problem then I will be pissed.