What is the code for p0420 p0491 p0492 on a Audi A6 2001?

The codes P0420, P0491, and P0492 on a 2001 Audi A6 indicate issues related to the vehicle's emissions system. Specifically, P0420 refers to "Catalyst System Efficiency Below Threshold (Bank 1)," while P0491 and P0492 are related to the secondary air injection system, indicating insufficient flow (P0491) and excessive flow (P0492). These issues can affect engine performance and emissions, often requiring inspection of the catalytic converter and the secondary air injection components. It's advisable to have a professional diagnose and address these codes for effective resolution.