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) (H6DO)>MAIN RELAY>INSPECTION .

   Is the check result OK?

   Yes: Go to  2 .

   No: Replace the main relay. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H6DO)>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 

   (E158) No. 60 - Chassis ground:

   (E158) No. 61 - Chassis ground:

   (E158) No. 62 - Chassis ground:

   (E158) No. 63 - Chassis ground:

   (E158) No. 64 - Chassis ground:

   (E158) No. 65 - Chassis ground:

   Is the resistance less than 5 Ω?

   Yes: Go to  3 .

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

   (B134) No. 27 (+) - 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 INPUT VOLTAGE OF MAIN RELAY  .

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

   Connector & terminal 

   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 main relay.
   3. Measure the voltage between ECM connector and chassis ground.

   Connector & terminal 

   (B134) No. 60 (+) - 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. 1 (+) - Chassis ground (-):

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

   Is the voltage 10 V or more?

   Yes: Check ignition control system. Ref. to ENGINE (DIAGNOSTICS) (H6DO)>DIAGNOSTICS FOR ENGINE STARTING FAILURE>IGNITION CONTROL SYSTEM .

   No: Repair the harness and connector.

   NOTE: In this case, repair the following item:

   • Open circuit in harness between ECM connector and main relay connector
   • Poor contact of main relay connector
   • Poor contact of ECM connector