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

Wiring diagram: 

Engine Electrical System Ref. to WIRING SYSTEM (IMPREZA MODEL)>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM . Ref. to WIRING SYSTEM (CROSSTREK MODEL (EXCEPT FOR HEV))>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM .

• IMPREZA MODEL

Courtesy of SUBARU OF AMERICA, INC.

• CROSSTREK MODEL

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) (H4DO (EXCEPT FOR HEV))>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) (H4DO (EXCEPT FOR HEV))>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  : Repair the harness and connector.

   NOTE: In this case, repair the following item:

   • Open circuit in harness between ECM connector and Chassis ground
   • Poor contact of coupling connector
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. 56 (+) - 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. 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 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 

      (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 (EXCEPT FOR HEV))>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 (EXCEPT FOR HEV))>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .