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

DTC detecting condition: 

Detected when two consecutive driving cycles with fault occur.

• Use the check board when measuring the ECM terminal voltage and resistance.

Wiring diagram: 

Engine Electrical System Ref. to WIRING SYSTEM>Engine Electrical System>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

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 MAIN RELAY CONNECTOR  .
   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. 38 - 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 main relay connector.

3. CHECK HARNESS BETWEEN ECM AND MAIN RELAY CONNECTOR  .
   1. Install the main relay.
   2. Turn the ignition switch to ON.
   3. Measure the voltage between ECM connector and engine ground.

      Connector & terminal 

      (B134) No. 12 (+) - Engine ground (-):

      (B134) No. 24 (+) - Engine ground (-):

   Is the voltage 10 V or more?

   Yes: Repair the harness and connector.

   NOTE: In this case, repair the following item:
   • Short circuit to power supply in harness between ECM connector and main relay connector
   • Defective main relay

   No: Repair the poor contact of ECM connector.