If you have an Audi S4, A8 or A6 with a 4.2 V8 with codes P1411 P1423 for secondary air insufficient flow this video maybe able to help you get started on your diagnostics. First, check your secondary air pump and the secondary air hoses this video shows you the common area the secondary air lines crack. It is always best to have an OBD scanner to clear the faults after performing a repair to give the on board diagnostics (OBD) system an opportunity to re-check itself.
Please feel free to ask a question in the comment section below if your are trying to diagnose and want another opinion, thanks ahead. Fault codes 17831, 17819 associated with this issue.
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