Check Mass Air Flow Sensor Unit

1. Connect the terminal No. 3 to the battery positive terminal and the terminal No. 4 to the battery ground terminal, the circuit tester positive terminal to terminal No. 5 and the circuit tester ground terminal to terminal No. 4.
   Fig 1: Connecting Terminal No. 3 To Battery Positive Terminal And Terminal No. 4 To Battery Ground Terminal

   Courtesy of SUBARU OF AMERICA, INC.
2. Check the voltage changes when air is blown to the mass air flow sensor unit in arrow direction.

Fig 2: Locating Mass Air Flow Sensor Unit

Courtesy of SUBARU OF AMERICA, INC.