M35x AWD V6-3.5L (VQ35DE) (2007)
Use a handy vacuum pump to check.
When connected to the booster side (1): Vacuum should decrease within 1.3 kPa (10 mmHg, 0.39 inHg) for 15 seconds under a vacuum of -66.7
kPa (-500 mmHg, -19.69 inHg).
When connected to the engine side (2): Vacuum should not exist.
^
Replace vacuum hose assembly if vacuum hose and check valve are malfunctioning.