I had a P0430 code for a long time. All my IM monitors passes but the secondary air. So I checked the air pump when engine is cold. I feel it blowing. I put a vacuum meter on the vacuum line to the valve and there's good vacuum.

I bought a foxwell NT510 and I activated the vacuum valve while the engine running and pump unplugged. I dont feel any exhaust coming out. I know my E53 2001 does not have a check valve. So exhaust should come out.

I removed the valve and I can see a lot of carbon. I cleaned it with throttle cleaner throughly. Put it back. Code did not clear. However 24hours later the CEL extinguished and all my IM monitors are "green".

I bought a replacement valve anyway, the amount of carbon in the port of the cylinder hear is about 1/4" thick, I dont know how to get that out.

Hope it helps someone. If you see all your IM monitors green except for secondary air, it might not be the cat.