Code 420 and 421 Isuzu Rodeo 2003

Question

I just change the cathalitic convertor for the therd time, I drove the car to work since last November, oly three months an the check engine came on with this codes PO 420 and PO 421
can some one sujest how to fix this problem? the car is a Isuzu Rodeo 2003.
Thanks for your help.
RODEO

Answer 1

P0420 Catalytic below threshold Bank 1

Is there any misfires, since the vehicle has been driven, Misfire are the number 1 cause of early catalytic convertor failure, the 2nd most popular especially with the Rodeo is that it burns oil. which coats the material of the catalytic convertor. At one time oil burning vehicle can be seen by the color of its blue smoke out the exhaust, with todays oil and its zinc property being removed, you dont see the blue smoke. A mechanical condition such as worn valves or coolant seepage into the combustion chamber, worn sparkplug ,