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Discussion Starter #1
My husband bought a used 2008 Wrangler on Fri. (78k miles). We had it inspected prior and was told it could be the O2 sensor or CC. The independent dealer put new ones (or maybe just 1 as I’m getting conflicting info from hubby) in on passenger side. We drove it home and no CEL. We went to dinner and it came on and had it checked at Autozone and it came up as PO430. Now, I’m so upset and have been trying to read all of these related threads - overwhelming.

What is the best course of action?
1. Get an OBD2 reader and pair it with one of the apps? Which app is best (apple)?
2. Go to a vendor who does exhaust work and get quote on CC replacement? Check first for any leaks and root cause or do I need to take it to a different place to have root cause checked?
3. Other?

We took a gamble on it being the O2 sensor and looks like that was dumb. Should we replace the other O2 sensors as well?

I’m sooo upset that he made a big mistake here, so trying to right the course yet. Thanks for any helpful feedback to save this situation.
 

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Replacing the O2 first is not dumb. They can fail for several reasons & it is a relatively cheap step in troubleshooting.



I used a basic ELM 327 OBD2 from eBay & Torque on my Android tablet for diagnosing when I had this.



Seemed to be either sensor or cat. I swapped the sensors left/right & the fault stayed on the same side, so that meant cats for me.
 

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I think replacing o2 sensors is a waste unless they are actually bad. Generally if you are getting P0420 or P0430 it's the Catalytic Converters. Its one of the few codes that actually isn't a starting point in diagnostics.

Now before you put new cats on, you do want to check O2 sensor function. You do this by monitoring the O2 sensors with a scan tool. You induce a rich condition by accelerating at full throttle. O2 sensors should go to .8v or higher. Then you introduce a lean condition by pulling a vac line. This should should see your o2 senors go really low...maybe .1v. If this happens your o2 sensors are working.

Other thing you can do is look at the rear o2 sensor in a bank and compare to the front. You should see the rear switching much less. If both the front and rear sensors switch at the same rate then your o2 has seen better days. When I say switching, it means the o2 sensor will switch from lean to rich, back and forth as the ECM controls the combustion process. The cat conv. will remove much of this switching in it's chemical process.
 

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Discussion Starter #5
Thank you for this info - checking it out. Planning to replace CC this week as a last resort, if needed
 

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Don't just blindly replace a cat. Bring your Jeep to a "real" mechanic who can check O2 operation, watching the signals. They should be able to diagnose exactly what's wrong. Things other than cats can set off 0420 and 0430 codes, including exhaust leaks.

It sounds like the seller is a slime ball and hit "reset all codes" on his OBD reader before selling you the car. 0430 will be the last monitor to go ready, so you get 10's of miles away at a minimum before that CEL pops on. In my state, 1 monitor not ready (max) will still pass inspection. Heck....I had a beater that I used that to wait for all the other monitors to go ready, get the car inspected and then had another year before I had to do anything.
 

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Now before you put new cats on, you do want to check O2 sensor function. You do this by monitoring the O2
Good info, thanks.
 

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I could clearly see the upsteam sensors cycling, but one downstream one doing it too. Swapped the downstream sensors & the fault remained on the same side. So as the upstream ones were ok, for me that was a cat, but as Jack FFR1846 said, there are other causes, like exhaust leaks letting air in before the sensors & messing the readings up.


Due to the cost of an OEM pipe for my 3.8 Down Under, I went whole hog & installed a stainless RIPP Long Tube Header full system for ~$1000 more than the stealer wanted for the OEM Y pipe, (including shipping from the US, 10% local GST, and having the headers ceramic coated to cut down the heat under the bonnet)...
 
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