check engine light and VSC lights are not on. The testing station said that the catalytic converters failed. If the converters were bad the lights should be on. I want to check/change the sensors first. Where is the sensor for the catalytic converter found? How do you change the sensor? Will a local auto repair shop know where to install and buy the sensors or do I have to go to the dealer?
My Lexus RX330 has 225K and runs fine except for the failed smog test.

 

Quite unusual, normally a code P0420 or/& P0430 or possibly others would appear...
You can try a bottle of CataClean for the time being if you have no codes, Google it, several mention success for passing emissions tests.

 

You really need techstream to read that check engine code. Because TS can tell if a sensor is failing or if the cat is failing. My last car before my RX was a Highlander which the cat did indeed fail but the readout for the codes on TS state "bank low efficiency" rather than "sensor circuit voltage low". Fortunately my Highlander was a 4 cylinder so only 1 cat to change whereas there are 2 in the RX (hopefully you only have one shot).