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 .

Fig 1: Engine Electrical System Wiring Diagram (ECM Power Supply And Ground Line Check)

Courtesy of SUBARU OF AMERICA, INC.

Fig 2: Engine Electrical System Diagnosis Flow Chart

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. 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 CONTROL MODULE  .
   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