Ford Repair: Service engine soon-Code P0420, ford escort zx2, walmart store

Question
I have a 2000 Ford Escort ZX2 car with mileage of 138792 on board. Today, while driving on expressway, I suddenly found "Service engine soon" on dash board which did not turn off afterwards (there is no blinking either). Since my oil exchange was overdue, I thought that may be the problem and changed my engine oil at the nearby Walmart store. But, this did not work and still I saw the service engine light during driving. So, I went to an AUTOZONE for further diagnosis of ECM. I was told by the AUTO ZONE people that the catalytic effective is low bank 1 (code P0420). They also suggested me that I need to change the Catalytic converter that may cost around $400 or so.  My car is still running fine and I don't think there is any problem with anything else. I need your opinion/suggestions. What should I do next? Because replacement of catalytic converter costs me a lot! Also, let me know how quickly I should fix the problem?


Answer
with your mileage it is very well possible you have a weak cat-you could also have a bad rear oxygen sensor both can be tested-now as for performance or other issues you shouldn't notice anything and you can have this repaired at your convenience or when your billfold can stand it-as long as your not in an area that requires emission inspections if you are then your car may not pass if check engine light is on. i will recommend one thing though if you do have a bad convertor replace with factory or a more expensive direct fit unit instead of a cheaper universal the latter have a tendency to not last very long it goes back to you get what you pay for. good luck