What does it mean?
The P0420 and the P0430 codes are caused by catalyst inefficiency. Replacing your catalytic converter is costly, so, knowing if a new catalytic converter is needed pays off. Your car’s exhaust system (below) comprises: a catalytic converter (s), at least two oxygen sensors and exhaust pipes that route the engine’s exhaust from the engine, through the catalytic converter, and out the car. The oxygen sensors sample your car’s exhaust before and after the catalytic converter.
In response to the amount of oxygen found in the exhaust, the oxygen sensors output a voltage which can be read with a multi-meter, oscilloscope, or scan tool. The oxygen sensor upstream of the catalytic converter will normally be referred to as Bank 2 O2 Sensor 1 (B2O2S1) and the downstream oxygen sensor will be Bank 2 O2 Sensor 2 (B2O2S2).