Coolant Shut-Off Valve
WARNING: This page is about a different car, the 2003 Volkswagen EuroVan and 2002 Volkswagen EuroVan. However, it is still accessible from the selected car via links, so may be relevant.
With engine off, vacuum supply to coolant shutoff valve is controlled by engine coolant 2 way vacuum valve. Valve allows coolant to circulate from engine to radiator when after-run coolant pump operates.