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

NOTE: After the faulty parts are repaired or replaced, perform the final check in Basic Diagnostic Procedure. Ref. to ENGINE (DIAGNOSTICS) (H4DO 2.0)>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .

Wiring diagram  :

Engine Electrical System Ref. to WIRING SYSTEM>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM>2.0 L MODEL .

G16764990Courtesy of SUBARU OF AMERICA, INC.
CAUTION: Use the check board when measuring the ECM terminal voltage and resistance. Ref. to ENGINE (DIAGNOSTICS) (H4DO 2.0)>GENERAL DESCRIPTION>PREPARATION TOOL>HOW TO USE CHECK BOARD .
  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)  .
    1. Turn the ignition switch to OFF.
    2. Remove the M/B (main relay 1).
    3. Check the M/B (main relay 1). Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>RELAY AND FUSE>INSPECTION>CHECK RELAY .

    Is the check result OK?

    Yes:  GO TO  3.

    No:  Replace the M/B (main relay 1). Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>RELAY AND FUSE .

  3. CHECK M/B (MAIN RELAY 2)  .
    1. Remove the M/B (main relay 2).
    2. Check the M/B (main relay 2). Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>RELAY AND FUSE>INSPECTION>CHECK RELAY .

    Is the check result OK?

    Yes:  GO TO  4.

    No:  Replace the M/B (main relay 2). Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>RELAY AND FUSE .

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

      Connector & terminal 

      (B62) No. 69 - Chassis ground:

      (B62) No. 70 - Chassis ground:

      (B62) No. 71 - Chassis ground:

      (B62) No. 72 - Chassis ground:

    Is the resistance less than 5 Ω?

    Yes:  GO TO  5.

    No:  Repair the harness and connector.

    NOTE: In this case, repair the following item:
    • Open circuit of harness between ECM connector and engine ground
    • Poor contact of coupling connector
  5. CHECK INPUT VOLTAGE OF ECM (SHORT TO GROUND)  .
    1. Turn the ignition switch to ON.
    2. Measure the voltage between ECM connector and chassis ground.

      Connector & terminal 

      (B62) No. 1 (+) - Chassis ground (-):

      (B62) No. 56 (+) - Chassis 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 M/B (MAIN RELAY 1) INPUT VOLTAGE  .

    Measure the voltage between M/B (main relay 1) terminal and chassis ground.

    Terminals 

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

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

    Is the voltage 10 V or more?

    Yes:  GO TO  7.

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

  7. CHECK M/B (MAIN RELAY 2) INPUT VOLTAGE  .

    Measure the voltage between M/B (main relay 2) terminal and chassis ground.

    Terminals 

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

    Is the voltage 10 V or more?

    Yes:  GO TO  8.

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

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

      Connector & terminal 

      (B62) No. 12 (+) - Chassis ground (-):

    Is the voltage 10 V or more?

    Yes:  GO TO  9.

    No:  Repair the open circuit of harness between ECM connector and M/B (main relays 1 and 2) terminal.

  9. 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 chassis ground.

      Connector & terminal 

      (B62) No. 67 (+) - Chassis ground (-):

      (B62) No. 68 (+) - Chassis ground (-):

    Is the voltage 10 V or more?

    Yes:  Check ignition control system. Ref. to ENGINE (DIAGNOSTICS) (H4DO 2.0)>DIAGNOSTICS WITH PHENOMENON>IGNITION CONTROL SYSTEM .

    No:  Repair the harness and connector.

    NOTE: In this case, repair the following item:
    • Open circuit or short to ground in harness between ECM connector and M/B (main relay 1) connector
    • Poor contact of M/B (main relay 1) connector
    • Poor contact of ECM connector
    • Blown out of fuse
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