P0420 code after i changed the cat converter, 54.6 miles, should i change the 02 sensorrs

I wood look at somin else clear the code if it comes back then we should seewhat we can do as anything Changes since it has been on ? Let me Know thks for your time

Those cars are notorious for engine problems unfortunately. The exhaust valves tend to warp from heat after around 200k miles. Therefore throwing the O2 codes. Best outcome and cost effective thing I can recommend is replacing the engine with a new or low mileage engine.

Yes, the leaking flex pipe could cause this code. You need to fix that, clear the code and re test. BUT: This vehicle has had issues with the catalytic converters coming apart and ruining the engine. It can suck catalytic converter pieces into the engine. When the converter is removed, visually inspect for damage.

this is what i found for you

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensorwaveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

Most likely, the aftermarket cat they installed is a high flow cat. This commonly causes issues with throwing that code on our cars. You can either have an OE cat installed, or just have the code deleted from the PCM by someone that has a tuner.
Good Luck

code p 0420 refers to cat converter system bank 1---efficiency below threshold====causes ---cat converter---wiring---HO2S (heated oxygen sensor, the one in the exhaust manifold before the cat converter)
code p 0300 is random misfires
I would suggest changing the HO2S as it reports to the ECM on exhaust content so that the ECM can adjust the air/fuel ratio
so it is logical that if that unit is not reporting correctly, the cat converter may be having trouble burning off the gasses correctly
The oxygen sensor(O2S) reads the results of the cat converter operation and helps fine tune the ECM settings

this is a catalyst efficiency code meaning your cars computer has indicated a problem with the flow of your catalytic converter located just after the exaust manifold i the exaust system, usally these codes are triggerd by a bad or "lazy" oxygen or O2 sensor, try replacing your 02 sensors if they have some miles on them and this may cure the problem, after the repair you will need to have the check engine light cleared by a shop or auto parts store

code --catalyst system efficiency below threshold bank 2 -means that the o2 sensor [bank 2 and after cat converter] is detecting that the converter in not working efficiently as it should as per specs--check the 02 sensor --if good possible exhaust leak if good --possible cat converter gone bad and since it is an 08 cat should be covered under warranty check with a dealer most converters are covered for five years doesnt matter how many miles on vehicle

If you don't have poor gas milage and loss of power, the cat is not restricted and not at fault, however, an engine misfire can also trigger that code.
Change the 02 sensor down by the cat first,( it's cheaper than a cat), see if that clears the code, if not, then go for the cat. You will already have a new 02 sensor, so that will eliminate those two. Hope this helped.

CODE PO420 CATALTYLIC CONVERTER SYSTEM FAULT.ITS SAYING FAULTY CATALTYLIC CONVERTER.IF IT BEEN A WHILE IF YOUR CAR HAS A WHOLE LOT OF MILES ON IT.YOUR SPARK PLUG CHANGE IS DUE AT 120000 MILES. DUE A LITTLE TUNE UP CHANGE AIR FILTER AND FUEL FILTER.SEE IF YOU HAVE ANY ENGINE FAULTS BAD PLUGS DIRTY INJECTORS ANY THING UP SET FUEL SYSTEM CAUSE CAR TO RUN RICH.EXCESSIVE UNBURN FUEL WILL GATHER IN CATALYTIC CONVERTER CAUSE IT TO BURN OUT.SHORTING LIFE OF THE CATALYTIC CONVERTER.

the light can be caused by any one or combination of over 200 trouble codes, go to any kragen or Autozone parts store and ask for a trouble code test, it is free, then record the code(s) they come up with and post them back on fixya