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

-
DTC detecting condition:

Detected when two consecutive driving cycles with fault occur.

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 .

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 .
1. 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.
2. 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).
3. 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.
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 .