Searched many of the threads with good diagnosis of the P0420 code but no real solutions.

I understand the 02 sensors are reading same. I just installed a new Dynomax Cat-back... is it possible that when hammering off the previous muffler (quite hard too) that I rattled or broke something within the Cat?

Any help is appreciated... Jeep runs excellent otherwise

1996 Country 4.0

 

I've got a '96 also. There was a recall for two potential problems. Cat converter and rear seatbelt anchors(I think). You can find out at this site if your converter was ever replaced. If not it's still covered. Not sure if your cat back system would void the recall or not. Worth a look though.

http://www.jeep.com/webselfservice/jeep/index.jsp

 

The P0420 code means the catalytic converter is at less than 95% efficiency. There is a recall for the exhaust on the 96 XJs.

 

installed new thermostat thinking my old one might be open full time, seafoamed the intake and reset the code... so far the code has not returned.. crossing fingers

 

cat faults almost always eventually return. some take months/ years some take two driving cycles. but chances are your 17 yr old cat probaly needs to be replaced. i also have a 96 but i dont have a rear 02 so theres no way to throw that fault.... i'm at least 90% sure i dont have one....