This bulletin applies to Audi A8 vehicles, where DTC P0491 (secondary air system bank 1, insufficient flow) and/or P0492 (secondary air system bank 2, insufficient flow) is detected. Because of an insufficient vacuum during the catalyst heating phase, the secondary air valves may close prematurely. Check the complete vacuum system for leaks.
Connect a hand vacuum pump with gauge on the marked point shown in Figure 1 (arrow).Check the connection between changeover valve N489 and vacuum regulator for the cylinder head coolant valve for leaks (Figure 2, arrow).
If no leak or fault is found, create a TAC ticket using the Technical Assistance Center System in ElsaWeb, including diagnostic log.
