How To Fix:Whistling Sound Under Hood

Applicable Vehicles :

• Volkswagon Golf GTI 2008-2012

How to tell if you have a problem :

This problem is pretty readily identifiable by a whistling sound coming from under the hood typically around 4000rpm, though it can present itself in other parts of the rpm range as well.  This can often times also cause a sudden loss in boost pressure.  Make sure it is coming from the valve itself and not a poorly tensioned or failing belt.

How to Fix Problem:

Typically replacing the unit with a "Revision D" diverter valve from VW can fix the problem.  Otherwise going with an aftermarket bypass valve can also rectify the issue.

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Definitions:

• Diverter Valve
  • Diverts excess intake tract pressure after closing the throttle performing similarly in function to a bypass valve or blow-off valve.