My Service Engine Soon will come on. on 1997 Buick Century

When I check the system with a scanner at my local mechanic the code that appears is PO420. This car has a 3.1 v6 with automatic transmission. If anyone has encountered the same problem please e-mail any suggestions to correct the problem. Thank you and may you have a Blessed Day.

1 answer 1 comment
P0420-catalyst below efficiency , have system (rear O2 sensor) monitored with scanner(NOT CODE READER!!!!!) to verify converter function. Clear code and see if it returns.
Thank you for your response,I will have the rear 02 sensor and cat.convertor serviced. Again Thank you and have a Blessed Day.