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

   Is the check result OK?

   Yes:  Go to  2.

   No:  Replace the 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 & terminal 

      (B134) No. 48 - Engine ground:

      (B134) No. 47 - Engine ground:

      (B134) No. 63 - Engine ground:

      (E159) No. 2 - Engine ground:

      (E159) No. 10 - 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 & terminal 

      (B134) No. 14 (+) - Engine ground (-):

      (B134) No. 54 (+) - 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 main relay.
   3. Measure the voltage between ECM connector and engine ground.

      Connector & terminal 

      (B134) No. 29 (+) - 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 & terminal 

      (B134) No. 15 (+) - Engine ground (-):

      (B134) No. 31 (+) - 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