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

Wiring diagram: 

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

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK FOR MALFUNCTION STATUS  .

   Check for the generating condition of starting failure.

   Is this a starting failure during Auto Start Stop?

   Yes

   Check the Auto Start Stop. Ref. to AUTO START STOP (DIAGNOSTICS)>BASIC DIAGNOSTIC PROCEDURE .

   No

   Go to  2 .

2. 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) (H4DO)>MAIN RELAY>INSPECTION .

   Is the check result OK?

   Yes

   Go to  3 .

   No

   Replace the M/B (main relay). Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>MAIN RELAY .

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

      Connector & terminal 

      (B134) No. 69 - Engine ground:

      (B134) No. 70 - Engine ground:

      (B134) No. 71 - Engine ground:

      (B134) No. 72 - Engine ground:

   Is the resistance less than 5 Ω?

   Yes

   Go to  4 .

   No

   Repair the following item.

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

      Connector & terminal 

      (B134) No. 1 (+) - Engine ground (-):

      (B134) No. 56 (+) - 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 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  6 .

   No

   Repair the open or ground short in the harness of power supply circuit.

6. 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 & terminal 

      (B134) No. 12 (+) - Engine ground (-):

   Is the voltage 10 V or more?

   Yes

   Go to  7 .

   No

   Repair the open circuit of harness between ECM connector and M/B (main relay) terminal.

7. CHECK INPUT VOLTAGE OF ECM  .
   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. 67 (+) - Engine ground (-):

      (B134) No. 68 (+) - Engine ground (-):

   Is the voltage 10 V or more?

   Yes

   Check the starter motor circuit. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>DIAGNOSTICS WITH PHENOMENON>STARTER MOTOR CIRCUIT .

   No

   Repair the following item.

   • Open circuit of harness between ECM connector and M/B (main relay) connector
   • Poor contact of M/B (main relay) connector
   • Poor contact of ECM connector
   NOTE: After the faulty parts are repaired or replaced, perform the final check in Basic Diagnostic Procedure. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .