Between intake manifold and vacuum pump

Remove the plug hole plate. (See PLUG HOLE PLATE REMOVAL/INSTALLATION [SKYACTIV-G 2.5T] .)
Remove the vacuum hose shown in the figure (between intake manifold and vacuum pump). (See VACUUM HOSE REMOVAL/INSTALLATION .)

Fig 1: Locating Vacuum Line Components
Courtesy of MAZDA MOTORS CORP.
Blow air into the vacuum hose (between intake manifold and vacuum pump) using your mouth from the vacuum pump side and verify that the air flows to the intake manifold side, then blow air from the intake manifold side and verify that the air does not flow to the vacuum pump side.

Fig 2: Check Valve Location

Courtesy of MAZDA MOTORS CORP.

If there is any malfunction in the check valve (between intake manifold and vacuum pump), replace it with the vacuum hose (between intake manifold and vacuum pump) as a single unit. (See VACUUM HOSE REMOVAL/INSTALLATION .)