So I have a 2003 is 300 and one day became sluggish we checked the codes and it said o2 sensors and the catalytic converter we we changed the header/ catalytic converter and all the 3 engine bay sensors and still the same next we change the catalytic converter and o2 sensors under the car and see if it fixes and suggestions???

 

What are the exact codes?

 

the codes is P0420

 

420 should be the manifold cats. Not O2 sensors at all. Did you use a brand new manifold or used?

 

yes I but a new one in and new senors now I'm going to change the cat under the car and sensor too

 

The cat under the car is after the O2 sensor. No reading on it. The only way it would effect the O2 readings. Would be if it is about clogged up all the way. If you are not in California. Just remove it or buy a Megan y pipe.

 

ok thank hope this helps