2018 Subaru Crosstrek Base, Automatic CVT TransFACTORY OEM SERVICE PROCEDURE

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

Wiring diagram: 

Engine Electrical System Ref. to WIRING SYSTEM (CROSSTREK MODEL)>Engine Electrical System>WIRING DIAGRAM .

G12400087Courtesy of SUBARU OF AMERICA, INC.
CAUTION: Use the check board when measuring the ECM terminal voltage and resistance. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>General Description>PREPARATION TOOL>HOW TO USE CHECK BOARD .
  1. CHECK M/B (MAIN RELAY)  .
    1. Turn the ignition switch to OFF.
    2. Remove the M/B (main relay).
    3. Connect the battery to M/B (main relay) terminals No. 2 and No. 4.
    4. Measure the resistance between M/B (main relay) terminals.

      Terminals 

      No. 1 - No. 3:

    Is the resistance less than 1 Ω?

    Yes:  Go to  2.

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

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

      Connector & terminal 

      (B134) No. 69 - Chassis ground:

      (B134) No. 70 - Chassis ground:

      (B134) No. 71 - Chassis ground:

      (B134) No. 72 - Chassis ground:

    Is the resistance less than 5 Ω?

    Yes:  Go to  3.

    No:  Open circuit of harness between ECM connector and engine ground terminal

  3. CHECK INPUT VOLTAGE OF ECM  .
    1. Turn the ignition switch to ON.
    2. Measure the voltage between ECM connector and chassis ground.

      Connector & terminal 

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

      (B134) No. 12 (+) - Chassis 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 chassis ground.

    Terminals 

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

    No. 2 (+) - Chassis 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. Turn the ignition switch to ON.
    4. Measure the voltage between ECM connector and chassis ground.

      Connector & terminal 

      (B134) No. 12 (+) - Chassis 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 KEYLESS ACCESS CM  .
    1. Turn the ignition switch to OFF.
    2. Connect the connector to ECM.
    3. Turn the ignition switch to ON.
    4. Measure the voltage between ECM connector and chassis ground.

      Connector & terminal 

      (B134) No. 67 (+) - Chassis ground (-):

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

    Is the voltage 10 V or more?

    Yes:  Check ignition control system. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>Diagnostics with Phenomenon>IGNITION CONTROL SYSTEM .

    No:  Repair the harness and connector.

    NOTE: In this case, 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 .
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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