My truck is kicking PO420 which also includes PO171 and PO174. I'm trying to diagnose are my cats going out or would it be the o2 sensors and is it causing the lean codes? This may have been posted before but I couldn't find a thread. Any help is appreciated.

 

Both are lean code, I'd figure those out first and then see if the cat code is still there after.

 

The PO420 code hit first the lean codes just happened. I have cleared the codes and checked what I could for the lean codes. I have even put the original intake tube and air filter housing back on to make sure my CAI didn't have a leak somewhere.

 

Check clamp on the throttle body of the cai they are infamous for coming loose especially if they have the rubber hose that rarely actually fits the throttle body with it.... P0171/p0174 are typical for intake gaskets leaking too.... P0420 couldve been caused by lean condition as well not enough variance between front and rear o2 on bank 1

 

Maybe a leak in the intake set up (vacuum lines, map sensor, etc)? Potentially an exhaust leak at the head or header flange?