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.

CAUTION: Use the check board when measuring the ECM terminal voltage and resistance.

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) (H4DOTC)>Main Relay>INSPECTION .
Is the check result OK?

Yes : Go to 2.

No : Replace the main relay. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>MAIN RELAY .
CHECK GROUND CIRCUIT FOR ECM (OPEN CIRCUIT) .
1. Disconnect the connector from ECM.
2. Measure the resistance of harness between ECM connector and engine ground.
  Connector & terminal
  
  (B134) No. 27 - Engine ground:
  
  (B134) No. 40 - Engine ground:
  
  (B134) No. 52 - Engine ground:
  
  (B134) No. 53 - Engine ground:
  
  (E158) No. 40 - Engine ground:
  
  (E158) No. 53 - Engine ground:
  
  (E159) No. 19 - Engine ground:
Is the resistance less than 5 Ω?

Yes : Go to 3.

No : Repair the following item.
- Open circuit of harness between ECM connector and engine ground
- Poor contact of coupling connector
CHECK INPUT VOLTAGE OF ECM (SHORT TO GROUND) .
1. Turn the ignition switch to ON.
2. Measure the voltage between ECM connector and engine ground.
  Connector & terminal
  
  (B134) No. 39 (+) - Engine ground (-):
  
  (B134) No. 46 (+) - Engine 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.
CHECK M/B (MAIN RELAY) INPUT VOLTAGE .
Measure the voltage between M/B (main relay) terminal and engine ground.

Terminals

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

No. 2 (+) - Engine 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.
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 engine ground.
  Connector & terminal
  
  (B134) No. 49 (+) - Engine 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.
CHECK HARNESS BETWEEN ECM AND M/B (MAIN RELAY) .
1. Connect the connector to ECM.
2. Turn the ignition switch to ON.
3. Measure the voltage between ECM connector and engine ground.
  Connector & terminal
  
  (B134) No. 13 (+) - Engine ground (-):
  
  (B134) No. 26 (+) - Engine ground (-):
Is the voltage 10 V or more?

Yes : Check the starter motor circuit. Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>Diagnostics with Phenomenon>STARTER MOTOR CIRCUIT .

No : Repair the following item.
- Open circuit of harness between ECM connector and M/B (main relay) terminal
- Poor contact of M/B (main relay)
- Blown out of fuse
- 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) (H4DOTC)>Basic Diagnostic Procedure>PROCEDURE .