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

Fig 1: Identifying Power Supply And Ground Line Of Engine Control Module (ECM) Wiring Diagram

Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTIC PROCEDURE FOR SYMPTOM

Step	Check	Yes	No
1 CHECK MAIN RELAY. Turn the ignition switch to OFF. Remove the main relay. Connect the battery to main relay terminals No. 1 and No. 2. Measure the resistance between main relay terminals. Terminals No. 3 - No. 5: No. 4 - No. 6:	Is the resistance less than 10 Ω?	Go to step 2 .	Replace the main relay. <Ref. to ELECTRICAL COMPONENT LOCATION .>
2 CHECK GROUND CIRCUIT FOR ECM. Disconnect the connectors from the ECM. Measure the resistance of harness between ECM and chassis ground. Connector & terminal (B134) No. 3 - Chassis ground: (B134) No. 5 - Chassis ground: (B137) No. 1 - Chassis ground: (B137) No. 2 - Chassis ground: (B137) No. 3 - Chassis ground: (B137) No. 7 - Chassis ground:	Is the resistance less than 5 Ω?	Go to step 3 .	Repair the open circuit of harness between the ECM and engine ground terminal.
3 CHECK INPUT VOLTAGE OF ECM. Measure the voltage between ECM and chassis ground. Connector & terminal (B135) No. 5 (+) - Chassis ground (-):	Is the voltage 10 V or more?	Go to step 4 .	Repair the open or ground short circuit of power supply circuit.
4 CHECK INPUT VOLTAGE OF ECM. Turn the ignition switch to ON. Measure the voltage between ECM and chassis ground. Connector & terminal (B135) No. 19 (+) - Chassis ground (-):	Is the voltage 10 V or more?	Go to step 5 .	Repair the open or ground short circuit of power supply circuit.
5 CHECK INPUT VOLTAGE OF MAIN RELAY. Measure the voltage between main relay connector and chassis ground. Connector & terminal (B47) No. 2 (+) - Chassis ground (-): (B47) No. 5 (+) - Chassis ground (-): (B47) No. 6 (+) - Chassis ground (-):	Is the voltage 10 V or more?	Go to step 6 .	Repair the open or ground short circuit of power supply circuit.
6 CHECK INPUT VOLTAGE OF ECM. Turn the ignition switch to ON. Measure the voltage between ECM and chassis ground. Connector & terminal (B134) No. 7 (+) - Chassis ground (-): (B135) No. 2 (+) - Chassis ground (-):	Is the voltage 10 V or more?	Check ignition control system. <Ref. to IGNITION CONTROL SYSTEM , Diagnostics for Engine Starting Failure.>	Repair the open or ground short circuit of harness between ECM and main relay connector.