My daughters 2001 s40 throwing above codes. Previously only would throw P0139 (cat efficiency code) but clear it and would go away for weeks. So is it bad MAF, O2 sensors or blocked up cat?

 

It very well could be the MAF. They do go bad eventually. But before spending money on one I'd try less costly fixes including MAF spray cleaner.

I've personally never heard of a clogged cat on these cars. I've had one on a mid 80's car but never with newer cars. From my experience the car will start and idle fine but have no power. You remove the upper O2 sensor and check if the car dramatically picks up power. Don't run it long like that as very hot exhaust gases are spewing into the engine compartment.

I'm thinking I'd first replace the upper O2 sensor and clear the codes then see how long it takes the codes to return. If the MAF is bad it should be pretty quick. If the MAF returns immediately then I'd replace it. Either way I'd order this: Oxygen Sensor Spacer (CEL Boss) which is placed between the lower O2 and the cat convertor. This will stop the code for bad convertor from returning.