What parts for error Code P0420

Hello Everyone,
Recently my 2003 double cab v6 threw a CEL. I got it diagnosed and is was the typical P0420 cat efficiency below threshold. I was unable to pick up my vehicle from the shop due to prior arrangements, so I didn't get all the information I wanted. Here is what the invoice says:

209005 engine light on, scanned and found P0420 cat efficiency below threshold. Tested no exhaust leak. Found O2 had power but was lazy switching.

Based on this, my plan of action is to swap out the upstream and downstream O2 sensors. Is this the correct course of action? Based on what is written here is there any indication a change of the Mass Air Flow sensor is needed, or the Catalytic Converter?

Thanks,
RT

 

Check fuel pressure. My 2nd gen started getting 420 and 430 codes. Fuel pressure was extremely low. A new fuel pump solved the problem. The low fuel pressure causes the bad O2 readings.

 

Do not switch upstream and downstream O2 sensors, they are different. The upstream one is actually an A/F sensor. I would try a new rear O2 sensor, but first check for exhaust leaks. How old are the catalytic converters?

 

Don't worry I would just swap them both with new o2 sensors. Im unsure about the cats but im pretty sure its stock. No leaks. Just some lazy o2 sensors but they didn't specify which one...

 

Fuel pressure test is easy and cheap/free, do it before you chase your tail...

 

where can I go to do a test?

 

Get a gauge and diy or take it to a shop and ask for a fuel pressure check?

 

I had P0420 and new downstream o2 took care of it