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

Wiring diagram:

Engine Electrical System Ref. to WIRING SYSTEM>ENGINE ELECTRICAL SYSTEM .

Courtesy 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 .

CHECK FOR MALFUNCTION STATUS .
Check for the generating condition of starting failure.

Is this a starting failure during Auto Start Stop?

Yes

Check the Auto Start Stop. Ref. to AUTO START STOP (DIAGNOSTICS)>BASIC DIAGNOSTIC PROCEDURE .

No

Go to 2 .
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)>MAIN RELAY>INSPECTION .
Is the check result OK?

Yes

Go to 3 .

No

Replace the M/B (main relay). Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>MAIN RELAY .
CHECK GROUND CIRCUIT FOR ECM .
1. Disconnect the connector from ECM.
2. Measure the resistance of harness between ECM connector and engine ground.
  Connector & terminal
  
  (B134) No. 69 - Engine ground:
  
  (B134) No. 70 - Engine ground:
  
  (B134) No. 71 - Engine ground:
  
  (B134) No. 72 - Engine ground:
Is the resistance less than 5 Ω?

Yes

Go to 4 .

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 .
1. Turn the ignition switch to ON.
2. Measure the voltage between ECM connector and engine ground.
  Connector & terminal
  
  (B134) No. 1 (+) - Engine ground (-):
  
  (B134) No. 56 (+) - 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 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 6 .

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 M/B (main relay).
3. Measure the voltage between ECM connector and engine ground.
  Connector & terminal
  
  (B134) No. 12 (+) - Engine ground (-):
Is the voltage 10 V or more?

Yes

Go to 7 .

No

Repair the open circuit of harness between ECM connector and M/B (main relay) terminal.
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 engine ground.
  Connector & terminal
  
  (B134) No. 67 (+) - Engine ground (-):
  
  (B134) No. 68 (+) - Engine ground (-):
Is the voltage 10 V or more?

Yes

Check the starter motor circuit. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>DIAGNOSTICS WITH PHENOMENON>STARTER MOTOR CIRCUIT .

No

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 .