P0411 - secondary air injection flow too low.
This is an easy system to test with a proper scanner. In activations the air pump is turned on and the O2 sensor voltage must go below 40mv in a short time. The typical problems involve the vacuum control of the airpump check valve, the air pump itself, the circuit to the air pump and the O2 sensor itself. This is not usually a piping problem.
The things you can do are to watch for the air pump working on a cold start and verify that the vacuum is reaching the check valve at that point and proceed from there.
Bosch Master, ASE Master, L1
33 years MB technician