Cats going bad? - JeepForum.com
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post #1 of 16 Old 06-13-2019, 05:13 AM Thread Starter
jeep63
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Cats going bad?

So my son's 06 LJ just threw an engine code for the Downstream Bank 2 O2 sensor. He also says he has to fill up more than usual.

I'm wondering if the cats are bad. Before I lay out 9-bills for a new set of cats, any ideas on troubleshooting ?

I did order 4 new O2 sensors, and now I'm considering ordering a new Cat. Magnaflow makes one that I have read good reviews for. It is pricey, but I hate exhaust work and if it bolts up I'll be pleased.

One benefit is when we bought it, the rear main and transmission cooler lines needed to be replaced, so the bolts are going to come out easily; at least easier than when they did for the rear main & tranny lines.



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post #2 of 16 Old 06-13-2019, 05:58 AM
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Replace pull O2 sensors and see if there is still catalytic material in your 2 pre cats. If there isn't I'd get new cats with O2 sensors

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post #3 of 16 Old 06-13-2019, 06:58 AM
ZEN357
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Replace the 02 sensors first. I had a vehicle that was drinking gas like a Saturday Night Binder and I replaced the 02 sensors and it went back to normal. I would try that first.

https://www.jegs.com/c/Jeep-Parts-Ac...05704/10002/-1
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post #4 of 16 Old 06-13-2019, 09:04 AM Thread Starter
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Replace pull O2 sensors and see if there is still catalytic material in your 2 pre cats. If there isn't I'd get new cats with O2 sensors

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Originally Posted by ZEN357 View Post
Replace the 02 sensors first. I had a vehicle that was drinking gas like a Saturday Night Binder and I replaced the 02 sensors and it went back to normal. I would try that first.

https://www.jegs.com/c/Jeep-Parts-Ac...05704/10002/-1
Thanks for the tips guys.

I have all 4 O2 sensors, the recommended ones (NGK)

We will try that first.


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post #5 of 16 Old 06-13-2019, 01:34 PM
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I would run a backpressure test on the exhaust system and a temp differential check also. If an upstream cat fails, it will easily restrict the lower cat.
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post #6 of 16 Old 06-13-2019, 03:10 PM
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Originally Posted by jeep63 View Post
I'm wondering if the cats are bad. Before I lay out 9-bills for a new set of cats, any ideas on troubleshooting ?
When my cat went bad it looked like this.
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post #7 of 16 Old 06-13-2019, 03:51 PM Thread Starter
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When my cat went bad it looked like this.
Now that is a 'Bad cat'!!!!
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post #8 of 16 Old 06-13-2019, 10:42 PM
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Quote:
Originally Posted by jeep63 View Post
So my son's 06 LJ just threw an engine code for the Downstream Bank 2 O2 sensor. He also says he has to fill up more than usual.

I'm wondering if the cats are bad. Before I lay out 9-bills for a new set of cats, any ideas on troubleshooting ?

I did order 4 new O2 sensors, and now I'm considering ordering a new Cat. Magnaflow makes one that I have read good reviews for. It is pricey, but I hate exhaust work and if it bolts up I'll be pleased.

One benefit is when we bought it, the rear main and transmission cooler lines needed to be replaced, so the bolts are going to come out easily; at least easier than when they did for the rear main & tranny lines.
what was the code? I'm guessing either P2096 or P2098

if it's one of those replacing the o2 sensors wont help and I doubt so will replacing the mini cats
I've been getting those codes for years, all I do is clear it with my scan gauge and continue on my way

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post #9 of 16 Old 06-14-2019, 12:49 AM
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Check for exhaust leaks upstream. That will also cause a downstream code.
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post #10 of 16 Old 06-14-2019, 03:33 AM
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Check for exhaust leaks upstream. That will also cause a downstream code.
Agreed, My TJ threw a Cat Code and I found that there were loose nuts where the exhaust attached to the exhaust manifold.
This causes excess air to enter the exhaust flow and the result is a cat code.
Problem was corrected.

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post #11 of 16 Old 06-14-2019, 04:10 AM Thread Starter
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The code was p0421.


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post #12 of 16 Old 06-14-2019, 04:13 AM Thread Starter
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Quote:
Originally Posted by Kolak View Post
Check for exhaust leaks upstream. That will also cause a downstream code.
Agreed, My TJ threw a Cat Code and I found that there were loose nuts where the exhaust attached to the exhaust manifold.
This causes excess air to enter the exhaust flow and the result is a cat code.
Problem was corrected.
I’ll also check the bolts.


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post #13 of 16 Old 06-14-2019, 07:24 AM
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ideally we want to use a scanner - check ALL codes, see what o2 sensors are reporting.

The exhaust leaks, exhaust back pressure checks, are good suggestions/

If you replace all o2 sensors you need to clear the RAM* As jeep calls it, NOT just clear codes.

All you need to do is remove Neg battery terminal


*POWERTRAIN VERIFICATION TEST VER - 5

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post #14 of 16 Old 06-14-2019, 01:34 PM
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I'm not going to prove or disprove your issue or claim I know what's happening. I just know my Jeep has thrown this code forever and with 5.13s and heavy (125lbs ea) 37s it still gets 14.5 mpg on the highway @70 (gps verified.) . I've had cats clog before. If you're flooring it to hold 60, you've got something up.


I don't have the issue on hand but there is a TSB out there referring to operating range of 02 sensors (I believe at start up)

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post #15 of 16 Old 07-08-2019, 04:56 AM Thread Starter
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Pre cats were clogged. Last night we pulled the original setup (127k miles) and installed Magna Flow's setup with the 4 new NGK sensors. The install was not too bad, but reaching the bolts at the exhaust manifold was tricky.


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