My 2004 MDX shows P0420 for bank 1 and bank 2. I have check the two catalyst converter and they are still very clean, just like brank new and you can easily see through them when you put it against sunlight. And I just changed the two oxygen sensors attached to bank 1.

History
Some weeks ago the car throw same code P0420 but just for bank 1, I loose the front one before finding out that that is bank 2, that bank 1 is the rear one, that was when I found out that the catalyst converters were okay, I changed the two O2 sensor attached to the Bank 1 catalyst, remove the battery head to clear the code.

seventeen (17) days later, I saw the engine light on with these code P0128, P0420 and P0420. P0128 is for thermostat, found out that my thermostat has failed open; I replaced the thermostat and remove the battery head to clear the code as usual. With some information I read online, that the P0128 fault code can also triggered P0420.

Now fourteen (14) days after, the code P0420 and P0420 for bank 1 and 1 came up. Don't know what to think off now, can the oxygen sensors be faulty and the system show code for catalyst.

The catalyst converter looks very okay from observation or do they expire.

Need your advice guys, getting confused here.