April 5, 2026: LEMON Manuals is launched! Read the announcement.

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

DTC detecting condition:

Detected when two consecutive driving cycles with fault occur.

CAUTION: After servicing or replacing faulty parts, perform Clear Memory Mode Refer to ENGINE (DIAGNOSTICS) (STI)>CLEAR MEMORY MODE>OPERATION ., and Inspection Mode Refer to ENGINE (DIAGNOSTICS) (STI)>INSPECTION MODE>PROCEDURE .

Wiring diagram:

Engine Electrical System Refer to WIRING SYSTEM>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM .

G12456948

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 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 ECM connector and chassis ground.
  Connector & terminal
  
  (B135) No. 13 - Chassis 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.
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 chassis ground.
  Connector & terminal
  
  (B136) No. 1 (+) - Chassis ground (-):
  
  (B137) No. 7 (+) - Chassis 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.