Happy New year to everyone. My 2011 XC60 T6 with 150K miles threw a P0420 code, my hand OBII wouldn't clear the code so I hooked up VIDA and sure enough the ECM fault code "Catalyst System Efficiency Below threshold (bank 1)" was there. Funny enough I was not able to delete the code using VIDA, most times a failing O2 sensor will throw this code and you can clear it and then the code will come on again somewhere in the imminent future but I can't understand why I can't clear it? When I click Erase All I get a communication fault message, car not responding? I'm assuming I will have to purchase a new downstream o2 sensor but can anyone shed any light on why I cannot clear the code?