I have a 2006 CTS with 2.8. Are the PCM and ECM two separate boxes and where are they located?
And can only a dealership reflash them? I want to try reflashing before buying new ones.

Any advice greatly appreciated.

This all stems from my previous post of everything on bank 1 not working.

I borrowed a Snap On OBD scanner from a great friend and it shows many codes including P0601, P0604 and P0606.