I'm at my wits ends here. I have a new engine new emission system and I'm still getting an EGR code p4020. I have a new 4.2 L V6 and the only thing I haven't changed is the intake manifold. The old one was in great shape and everything was tight.

 

What may be needed here is a capable scan tool to obtain the data stream info. From that we can have a better idea of just what is going on.

A defective oxygen sensor can affect catalytic converter function as a defective converter can affect oxygen sensor function. The idea is to examine the info and see which is under performing..