2004 325i sluggish with P0411 code

Hello, I have a 2004 325i with 72,000 miles that has SES light on. I scanned it and pulled the P0411 code, Secondary Air Injection System Incorrect Flow Detected. I have tried re-setting, but it keeps coming back. This car has also seemed pretty sluggish recently. I understand that there is an air pump, solenoid valve, and O2 sensors in this system. I know that I can listen for the pump running when I start the car. Does the engine need to be just cold (not running recently) or does it have to be wintertime temperature for the system to try to operate? Also, is there a way I can test the O2 sensor? Is there anything else I am missing? I have read about a carbon build-up issue causing this problem in M5 engines? Your help is appreciated!

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