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, 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
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: Locating Area To Blow Air Into Mass Air Flow Sensor Unit
Courtesy of SUBARU OF AMERICA, INC.