Check The Mass Air Flow Sensor Unit

Connect the battery positive terminal to terminal No. 1 and the battery ground terminal to terminal No. 2, and connect the circuit tester positive terminal to terminal No. 3 and the circuit tester ground terminal to terminal No. 2.

Fig 1: Checking Mass Air Flow Sensor Unit Terminals Voltage
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: Mass Air Flow Sensor Unit Air Flow Direction

Courtesy of SUBARU OF AMERICA, INC.