Join Date: Jan 2004
Location: Neenah, WI
Car: MY12 WRX, MY07 FXT
Feedback Score: 0 reviews
^Well personally I have never heard of a front O2 sensor being replaced due to that code.
I did just find basic info on the PO420:
My check engine light came on and my mechanic said the Catalytic Converter was the problem. How can I be sure?
This has been a tricky problem for most mechanics and exhaust shops, When diagnosing the problem with a scan tool. The code that comes up for an inefficient Catalytic Converter is a PO420. This is an indication that the Catalytic Converter is not doing its job properly but we have found that this code could also occur if the Oxygen Sensor (O2 Sensor) or sensors become faulty or lazy, We have also found that on the Jeep Cherokee, Subaru Outback, Ford Explorer and Honda Accord, the factory tolerances that set off the check engine light are very tight and an engine that has carbon buildup in the combustion chamber will bring up the cylinder head temperature which in turn brings up the Oxides of Nitrogen (NOX) and will set the light off. In these cases we recommend a product on the market that has been working well to cut down on the carbon build up and will reduce the dreaded check engine light and PO420 code. The product is called BG44K- Total Deposit Control Fuel Additive and can be purchased from us at our product link. A good rule of thumb here is to make sure all components that we have mentioned here have been checked before the Catalytic Converter is replaced. There is nothing worse than spending hard earned money on a Catalytic Converter and find out that the check engine light problem still exists.
A decent quick read that I found.
If you can't see into the future, you aren't driving fast enough