Code PO 420

[Bill C.]

Hi everybody, newbie to the forum. I have a 2001 GMC Yukon XL, had a service engine soon light come on the other day. Pulled the code, and it was a PO420, catylist effiencincybelow threshold ( bank 1). O2 sensor, or converter? I'm thinking O2 sensor, just wanting input. Be talking again to you soon. :thumbsup:

 

[u2nv]

1. is there any other codes set if no step 2 if yes diag those first, 2. any exhaust leaks fix those first real common for broke exhaust manifold bolts there is new style bolts with updates to torque specs,3. if all above ok replace cat that shows low effic either bank 1 or 2. hope this helps