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

Engine Electrical System ENGINE TYPE FB (WITHOUT PUSH BUTTON START) < Ref. to appropriate wiring diagram in SYSTEM WIRING DIAGRAM article. >
Engine Electrical System ENGINE TYPE FB (WITH PUSH BUTTON START) < Ref. to appropriate wiring diagram in SYSTEM WIRING DIAGRAM article. >

Fig 1: Engine Control Module (ECM) Power Supply And Ground Line - Wiring Diagram
Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTIC PROCEDURE

Step	Check	Yes	No
1 CHECK M/B (MAIN RELAY). Turn the ignition switch to OFF. Remove the M/B (main relay). Connect the battery to M/B (main relay) terminals No. 2 and No. 4. Measure the resistance between M/B (main relay) terminals. Terminals No. 1 - No. 3:	Is the resistance less than 1 Ω?	Go to step 2 .	Replace the M/B (main relay). < Ref. to MAIN RELAY . >
2 CHECK GROUND CIRCUIT FOR ECM. Disconnect the connector from ECM. Measure the resistance of harness between ECM connector and chassis ground. Connector & terminal (E158) No. 61 - Chassis ground: (E158) No. 62 - Chassis ground: (E158) No. 63 - Chassis ground: (E158) No. 64 - Chassis ground: (E158) No. 65 - Chassis ground:	Is the resistance less than 5 Ω?	Go to step 3 .	Open circuit of harness between ECM connector and engine ground terminal
3 CHECK INPUT VOLTAGE OF ECM. Turn the ignition switch to ON. Measure the voltage between ECM connector and chassis ground. Connector & terminal (B134) No. 2 (+) - Chassis ground (-): (B134) No. 27 (+) - Chassis ground (-):	Is the voltage 10 V or more?	Go to step 4 .	Repair the open or ground short in the harness of power supply circuit.
4 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?	Go to step 5 .	Repair the open or ground short in the harness of power supply circuit.
5 CHECK INPUT VOLTAGE OF ECM. Turn the ignition switch to OFF. Install the M/B (main relay). Turn the ignition switch to ON. Measure the voltage between ECM connector and chassis ground. Connector & terminal (B134) No. 60 (+) - Chassis ground (-):	Is the voltage 10 V or more?	Go to step 6 .	Repair the open circuit of harness between ECM connector and M/B (main relay) terminal.
6 CHECK INPUT VOLTAGE OF ECM. Turn the ignition switch to OFF. Connect the connector to ECM. Turn the ignition switch to ON. Measure the voltage between ECM connector and chassis ground. Connector & terminal (B134) No. 1 (+) - Chassis ground (-): (B134) No. 14 (+) - 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 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