This is a 2008 JKU Sahara. I'm at 103K miles so the warranty has expired on the catalytic converters, but I have the Unlimited Powertrain Warranty, so the exhaust manifolds are covered.

I know what the codes are, and what the possible causes and solutions could be, but I'm hoping to narrow it down since I get both codes at the same time.

Before this code, I also had the P0300, but have changed plugs and wires and haven't received it again.

I'm looking to trade the Jeep in so I'm looking for the most inexpensive fix. Any help is appreciated.

P0420 Error Code: Catalyst System Efficiency Below Threshold (Bank 1)

 

Since you know what the possible causes are, the cheapest way to proceed is to make a list of all the possible causes that don't require special tools or new parts to troubleshoot, and start knocking those item out. Those items won't cost you anything to find, and may be a simple, almost free fix.

How long did you have the misfire? If it was for quite a while, that could have damaged your cats.

 

Thanks for the response. You're on every thread I eat on this topic.The misfire happened twice before I changed the plugs and wires. I just didn't know if both codes at the same time were uncommon and would help to isolate the problem.

 

Have you replaced any of the O2 sensors recently?

 

No. Everything is original except for the Dynomax catback.

 

The PO420 code is the code to smoke some before you look at the PO430 code because it is gonna piss you off!

 

I have a 08 jk with po430, please help it has 200k km

 

I had the P0430 and in my case it was a cracked driverside exhaust manifold 254,000klm ..

 

First off, Im located in CA. I have the dreaded 0420/0430 codes showing. I have recently tuned the vehicle, replaced both exhaust manifolds, replaced o2 sensors and still get the codes. The Jeep has 223k on it and runs great. no hesitation, idles smooth. I hooked up a scanner and the o2 sensors appear to be operating correctly. no rattles from under the car. can it still be the cats? im dreading this as there is no aftermarket cats avail. dealer only. 1200 for the part alone. any suggestions?