My Audi or VW's check engine light is on

If the valve does not make a whoosh noise, or a fluttering sound is heard when shifting gears, check the orientation of the valve. Note that a GFB valve MUST be installed in the reverse direction to the factory diverter. If you are unsure, simply swap it around anyway and try it.

If the valve does actually make a whoosh sound when shifting gears, increase the spring pre-load 1 turn at a time until the check engine light turns off. You will find that the valve does not vent as much at lower RPM, and you may hear a flutter in this case. Rest assured this does NOT damage the turbo.

There will quite often be some low-rpm flutter with an aftermarket BOV installed, since they work differently to a factory valve in order to allow them to vent to the atmosphere and make the blow-off whoosh.