I recently got a check engine light telling me that the O2 sensors had issues so I replaced them. The problem persistent, took it to make dealer and told it was the AF Sensors. I then replaced those and again the problem appeared. Now, I'm told that the Catalytic converters need to be replaced. However, one mechanic told me that I should also replace the sensors that I had recently put in. Do I need to replace the sensors again? I have purchased the Cat Converters but have not installed them until I know if the extra cost and work is also necessary. Appreciate any help. Thanks.
Personally, I would change just the catalysts. Change one thing (or one group of things) at a time. If it fixes the issue you're good to go. If not there are ways to test sensors that don't include replacing them. The service manual or the internet will give you detailed instructions for testing the sensors.
Did the mechanic offer a benefit for changing everything at once or replacing new parts? Emissions parts are generally pretty simple in operation and quite durable. Replacing them after a short time in service seems wasteful.
US vehicles are required to carry an 8 year/80K mile warranty on major emission components. Far greater than they provide on the rest of the vehicle.