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DTC P0685: ECM/Pcm Power Relay Control Circuit/Open: Notes

DTC detecting condition:

Detected when two consecutive driving cycles with fault occur.

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 .

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 .

Wiring diagram:

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

G13891321

Courtesy of SUBARU OF AMERICA, INC.

CHECK ECM CONNECTOR .
Check the connecting condition of ECM connector.

Is the ECM connector correctly connected?

Yes: Go to 2.

No: Connect the ECM connector correctly.
CHECK HARNESS BETWEEN ECM AND M/B (MAIN RELAY) (SHORT TO GROUND) .
1. Turn the ignition switch to OFF.
2. Remove the main relay.
3. Disconnect the connector from ECM.
4. Measure the resistance between the ECM connector and engine ground.
  Connector & terminal
  
  (B134) No. 12 - Engine ground:
Is the resistance 1 MΩ or more?

Yes: Go to 3.

No: Repair the short circuit to ground in harness between ECM connector and M/B (main relay).
CHECK HARNESS BETWEEN ECM AND M/B (MAIN RELAY) (SHORT TO POWER SUPPLY) .
1. Turn the ignition switch to ON.
2. 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: Repair the short circuit to power supply in harness between ECM connector and M/B (main relay).

No: Go to 4.
CHECK MAIN RELAY .
1. Turn the ignition switch to OFF.
2. Check the main relay. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>MAIN RELAY>INSPECTION .
Is the check result OK?

Yes: Repair the poor contact of ECM connector.

No: Replace the main relay. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>MAIN RELAY .