Two-Way Valve
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2003 Hyundai XG350, 2003 Hyundai Tiburon, 2003 Hyundai Sonata, 2003 Hyundai Santa Fe, and 2003 Hyundai Elantra. However, it is still accessible from the selected car via links, so may be relevant.
Apply vacuum to inlet side and then to outlet side of two-way valve. Vacuum applied to inlet side of two-way valve should hold. Vacuum applied to outlet side of two-way valve should not hold. Replace two-way valve if operation is not as specified.