P0420, Changed parts but light keeps coming back.
 

Ok, so I popped a P0420 Catalyst efficiency below threshold bank 1. I have changed my EGR valve, both O2 sensors, Cat and the muffler. The only thing I have not changed is the Pre-muffler.

I have taken the ECM fuse out and reset it twice also. The light stays off for about 3-5 days and comes back on. I have come to the conclusion I may have a bad CAT but what are the odds of a new converter being bad?

I would appreciate any thoughts or input....

cheap cat converter?

I bought it through rockauto.com I did not buy the cheapest sat converter. But my thought on this is the converter is bad. Do you suggest changing the pre muffler to?

I live in Germany and the OG parts or aftermarket parts for that matter are insanely eexpensive here.

I have no idea what part quality u have on there