So I’ve been getting a P0420 catalytic converter loss of efficiency. Replaced the O2 sensors and code still comes back. Does this mean I just need to replace the cats or is there something else I could be missing? Also, has anyone had any luck with aftermarket cats or is it best to just stick with Mopar OEM part. I ask because that OEM Cat is very pricy compared to other aftermarket brands.

 

P0420's title is CATALYST EFFICIENCY (BANK 1), but there is a lot to look at before condemning the cat, which is last on the list.
The circuits for either O2 sensor could be open, or shorted to ground.
An exhaust leak could be the cause.
A mechanical issue with the engine is also a possibility.

Lately, my '08 JK has thrown codes for O2 sensors, the ABS system, and the evap system.
The cause each time has been related to bad ground connections in each circuit. Cost to fix has been nearly $0.

 

Well I haven’t had any other codes other than P0158 sensor 2/bank2. That code stopped when I replaced all the O2 sensors. Still getting the P0420. No engine issues but an exhaust leak might not be out the question I do hear a pft sound from the engine bay.

 

It may be a mechanical issue upstream of the cats, but if you can't determine the cause, before you start throwing money at this, try a couple of bottles of Cataclean and see if the P0420 code goes away. I had that code and the O2 sensor code happen a few miles after buying some bad gas. Took it into the dealer and they wanted $3600 to replace all cats and O2 sensors. I passed on that and tried the Cataclean and it took care of the issue. Maybe my situation is an exception, but for $50, it's worth a try.

 

I had same issues on my 08 a few years back. The drivers side cat ended up being bad. Throw an infrared thermometer at it and see how hot it is at normal operating temps. My guess is it’s cooking. I’m not sure what the favorable temp is...1000-1200ish I’d assume. Mine was pushing 1400! She was toasted. Of course I tried cataclean, sea foam etc first hoping to save money. I ended up buying a full y-pipe for 450+/- and changed myself in the driveway. Then I sold my cats for $150. Good luck.