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

Wiring diagram:

Engine Electrical System Refer to WIRING SYSTEM (IMPREZA MODEL)>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM . Refer to WIRING SYSTEM (CROSSTREK MODEL (EXCEPT FOR HEV))>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

CAUTION: Use the check board when measuring the ECM terminal voltage and resistance. Refer to ENGINE (DIAGNOSTICS) (H4DO (EXCEPT FOR HEV))>General Description>PREPARATION TOOL>HOW TO USE CHECK BOARD .

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). Refer to FUEL INJECTION (FUEL SYSTEMS) (H4DO (EXCEPT FOR HEV))>MAIN RELAY>INSPECTION .
Is the check result OK?

Yes: Go to 2.

No: Replace the M/B (main relay). Refer to FUEL INJECTION (FUEL SYSTEMS) (H4DO (EXCEPT FOR HEV))>MAIN RELAY .
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: Repair the harness and connector.
NOTE:
In this case, repair the following item:
- Open circuit in harness between ECM connector and Chassis 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 chassis ground.
  Connector & terminal
  
  (B134) No. 1 (+) - Chassis ground (-):
  
  (B134) No. 56 (+) - 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.
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.
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 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.
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. 67 (+) - Chassis ground (-):
  
  (B134) No. 68 (+) - Chassis ground (-):
Is the voltage 10 V or more?

Yes: Check ignition control system. Refer to ENGINE (DIAGNOSTICS) (H4DO (EXCEPT FOR HEV))>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

NOTE: After the faulty parts are repaired or replaced, perform the final check in Basic Diagnostic Procedure. Refer to ENGINE (DIAGNOSTICS) (H4DO (EXCEPT FOR HEV))>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .