po420 code

My 2001 Malibu 3.1L keeps getting the po420 code. I replaced the converter 3 times and replaced both o2 sensors. I had the fuel system checked. Fuel pressure 70psi without vac and 60psi with vac. I still keep getting this code. Please help!

Welcome to AF, this can be a complex issue to diagnose. do a site search and you will find lots of info. 60 psi seems high?

P0420 = Catalyst System Efficiency Below Threshold (Bank 1) There's only 2 things that can cause this: A cat that needs to be replaced or it's downstream O2 sensor needs to be replaced. I have seen P0420's thrown on newer cars that eventually clear and dont come back. Unless you've got a ton of miles on your 2001, or burned lots of coolant or other things that should not be combusted, a cat should not have soured on a 2001. There are two catalytic converters on a 3.1. Bank 1 and bank 2. Are you sure the bank 1 cat was replaced and not the #2? There also should be 4 oxygen sensors on the 2001 3.1L. One before each cat and one after each. The after cat sensors are there to set the P0420 and P0430 codes only. They serve no other purpose. Just go/no-go gauges.

Joel