P0420 Cadillac - 2004 Deville

Question

I replaced the catalytic convertor and erased the code, but P0420 re-indicates. Based on the extensive info you have provided, I believe I need to replace the HO2S located between the cat and the resonator. Is there anything else I should consider before replacing this sensor/monitor? Thanks, Mike

Answer 1

P0420 Catalytic below efficiency Bank 1

Fuel control, if the engine is in fuel control the catalytic will work in order for the catalytic to work properly the 02 sensor both of the upstream need to work properly this mean the 02 sensor needs to see a rich running condition and a lean running condition this is a lean to rich cycle at .5 hertz to 5 hertz. and  is not bias lean or bias rich which would be a failing degraded 02 sensor, and there should not be any misfire or vacuum leaks which will cause a lean condition and it does not need to cause a lean code condition to appear. Good sparkplugs good sparkplug wires clean airfilter and do a MAF (mass airflow) cleaning with a throttle body cleaning. This code may be a intermittent as the catalyst material needs to degass.