Check The Mass Air Flow Sensor Unit

WARNING: This page is about a different car, the 2012 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.

Connect the battery positive terminal to terminal No. 3 and the battery ground terminal to terminal No. 4, the circuit tester positive terminal to terminal No. 5 and the circuit tester ground terminal to terminal No. 4.

Fig 1: Connecting Battery Positive Terminal To Terminal No. 3 And Battery Ground Terminal To Terminal No. 4
Courtesy of SUBARU OF AMERICA, INC.
Check the voltage changes when air is blown to the mass air flow sensor unit in arrow direction.

Fig 2: Checking Voltage Change For Mass Air Flow Sensor
Courtesy of SUBARU OF AMERICA, INC.