I have a 2003 Ford Fiesta Mk6 1.4 petrol.

A short while ago my engine management light came on. I took the car immediately to a local Ford dealer.

They told me it needed a new catalytic converter. I could not afford their prices at the time and so took the car away.

Two days later the engine management light went off and has stayed off. The car seems to be running fine.

I haven't replaced the catalytic converter.

Does this mean the catalytic converter is OK? Do they correct themselves or is it something more serious?

 

It was probably a P0420 code which compares the pre and post cat hego sensors , if the post one still shows big changes in oxygen content it throws up the code as it assumes the cat is no longer working , but I have had this code come on for no reason , it may come back on as it could be on a warm up cycle and it did not get up to temp so was not very efficient and the light came on , but after several drive cycles it will self extinguish as it has not seen the same fault on those cycles .

 

This code is not set without a reason. In 99% of the cases the catalyst has died.
The remaining 1% can be caused by mixture problems, but not by a fault in the rear oxygen sensor.
Is there any history of misfires, failing injectors, coils, etc.?
Have you lost cooling fluid lately, or oil?