P0420 Pontiac - What to do next?

Question

I have a G6 and P0420 code pops up. I have changed the catalytic converter and both upstream and downstream 02 sensor. I also put in some guarantee to pass thinking that it may blow out the system. I can not figure out what to do next. Also checked to see if the maf sensor is working. Please help me out and try to help me solve this problem? Thanking you in advance James

Answer 1

P0420 Cataytic below threshold Bank 1

Where did you get this catalytic convertor?, at one time the dealer issued a Recall for the catalytic convertor. The best way to resolve this is to use a scan tool to check the fuel trim. and the catalytic convertor using the 02 sensor , Bank 1 Sensor 2 is for the downstream 02 sensor or catalytic monitor sensor.

 Here a scan tool with a data using a graph, Bank 1 Sensor 2 this is the downstream 02 sensor or the catalytic monitor sensor A good catalytic would have the rear 02 sensor staying above 650 mv.  This is a bad catalytic convertor as the rear 02 sensor see this as 520mv if this reading stay there long enough a P0420 will occur