Fault Code Help Please

[lenny123]

Hi guys i need your help i have just been on way home after work and my engine check light came on so i got my reader out with luckly was in my boot and i got a stored code of P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK 1 . i have just had my original exhaust put back on yesterday as my japspeed one was to loud for me so i am hoping you guys can help with what the problem could be it took 50 miles for the light to come on and when i hold my hand tight on the end of the exhaust i can hear a slight blow near the mid cat could a gas leak from a blowing joint cause this code to come up thanks for any help.

[mattc]

I had a similar fault when I had a new centre sectino fitted, and a few weeks alter it was blowing and coming up with ECU error codes.

I say check all the joints first