Make an appointment for next week?

As required, you didn't say what car you have or how old it is, how many miles are on it, etc.
Since you're in the SX4 forum section I can only guess that you're driving some form of an SX4, 2007 or 2008. Am I close?
And, that you probably have not driven far enough to exceed the life expectancy of your Catalytic Converter. Eh?



Afterthought....
I'm curious just how the Engine control computer is coming up with that conclusion. ??? Is it measuring back pressure, maybe?
Because, to my knowledge, there are no more sensors down-stream from the catalytic converter.

If you can, check your exhaust system to make sure that something has not damaged your exhaust pipe, muffler or tail pipe that would increase the back pressure on the engine.

 

There is an O2 sensor downstream of the CAT, it measures the exhaust after the combustion in the CC.

Info.. P0420 Error Code: Catalyst System Efficiency Below Threshold (Bank 1)

Dependent on age and mileage there might still be warranty coverage (emissions)

 

I guess I'm thinking of the older CC's that were further back under the car and there were NO sensors on them.
I'm always glad to learn something new.

Thanks for the info.