Air sucking Audi
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.
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| Figure 1: Vacuum system. (A) Operation of left charge-motion control valve. (B) Operation of right charge-motion control valve. (C) Operation of intake manifold control valve. (D) Left secondary air valve. € Right secondary air valve. (F) Electric changeover valve for engine thermo management (coolant valve on cylinder head). (1) Vacuum from intake manifold. (2) Vacuum reservoir of cylinder head. (3) Vacuum reservoir in inner V. |
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| Figure 2: Vacuum hose not connected. |
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