Check Mass Air Flow Sensor Unit

Connect battery positive terminal to terminal No. 3 and battery ground terminal to terminal No. 4, circuit tester positive terminal to terminal No. 5 and the circuit tester negative 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 that the voltage changes when air is blown to the mass air flow sensor unit from arrow direction.

Fig 2: Locating Mass Air Flow Sensor Unit
Courtesy of SUBARU OF AMERICA, INC.