Check Power Supply And Ground Line Of Engine Control Module (ECM)

Wiring diagram: 

Engine Electrical System Ref. to WIRING SYSTEM>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK M/B (MAIN RELAY). 
   1. Turn the ignition switch to OFF.
   2. Remove the M/B (main relay).
   3. Check the M/B (main relay). Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>MAIN RELAY>INSPECTION .

   Is the check result OK?

   Yes  : Go to  2.

   No  : Replace the M/B (main relay). Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>MAIN RELAY .

2. CHECK GROUND CIRCUIT FOR ECM (OPEN CIRCUIT). 
   1. Disconnect the connector from ECM.
   2. Measure the resistance of harness between ECM connector and engine ground.

      Connector and terminal. 

      (B134) No. 27 - Engine ground:

      (B134) No. 40 - Engine ground:

      (B134) No. 52 - Engine ground:

      (B134) No. 53 - Engine ground:

      (E158) No. 40 - Engine ground:

      (E158) No. 53 - Engine ground:

      (E159) No. 19 - Engine ground:

   Is the resistance less than 5 Ω?

   Yes  : Go to  3.

   No  : Repair the following item.

   • Open circuit of harness between ECM connector and engine ground
   • Poor contact of coupling connector
3. CHECK INPUT VOLTAGE OF ECM (SHORT TO GROUND). 
   1. Turn the ignition switch to ON.
   2. Measure the voltage between ECM connector and engine ground.

      Connector and terminal. 

      (B134) No. 39 (+) - Engine ground (-):

      (B134) No. 46 (+) - Engine ground (-):

   Is the voltage 10 V or more?

   Yes  : Go to  4.

   No  : Repair the open or ground short in the harness of power supply circuit.

4. CHECK M/B (MAIN RELAY) INPUT VOLTAGE. 

   Measure the voltage between M/B (main relay) terminal and engine ground.

   Terminals. 

   No. 1 (+) - Engine ground (-):

   No. 2 (+) - Engine ground (-):

   Is the voltage 10 V or more?

   Yes  : Go to  5.

   No  : Repair the open or ground short in the harness of power supply circuit.

5. CHECK INPUT VOLTAGE OF ECM. 
   1. Turn the ignition switch to OFF.
   2. Install the M/B (main relay).
   3. Measure the voltage between ECM connector and engine ground.

      Connector and terminal. 

      (B134) No. 49 (+) - Engine ground (-):

   Is the voltage 10 V or more?

   Yes  : Go to  6.

   No  : Repair the open circuit of harness between ECM connector and M/B (main relay) terminal.

6. CHECK HARNESS BETWEEN ECM AND M/B (MAIN RELAY). 
   1. Connect the connector to ECM.
   2. Turn the ignition switch to ON.
   3. Measure the voltage between ECM connector and engine ground.

      Connector and terminal. 

      (B134) No. 13 (+) - Engine ground (-):

      (B134) No. 26 (+) - Engine ground (-):

   Is the voltage 10 V or more?

   Yes  : Check the starter motor circuit. Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>DIAGNOSTICS WITH PHENOMENON>STARTER MOTOR CIRCUIT .

   No  : Repair the following item.

   • Open circuit of harness between ECM connector and M/B (main relay) terminal
   • Poor contact of M/B (main relay)
   • Blown out of fuse
   • Poor contact of ECM connector