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 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) (H4DO)>MAIN RELAY>INSPECTION .
Is the check result OK?

Yes : Go to 3 .

No : Replace the 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 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)
- Poor contact of M/B (main relay)
- 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 .

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

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

Use the Manual With the Right Hardware

When to See a Mechanic