Hi

My partners 2005 1.6 Golf keeps throwing P0420 code 0420 “Catalyst System Efficiency Below Threshold (Bank 1).”

I’ve changed the cheapest parts first, O2 sensors have been changed, throttle body cleaned, coil packs and plugs changed. But keeps throwing the code. When its turned off, it might not come back for another 80miles.

Would this be the front cat or the middle bit?

Thanks