P0685

Symptoms

• The engine does not start or stalls immediately after starting
• Check Engine Light
• Complete absence of signals from the ECU
• Unstable engine operation
• Spontaneous engine shutdown

Causes

• Open circuit control circuit of the ECU power relay coil
• ECU power relay malfunction
• Oxidation or damage to the relay connector
• Damage to the wiring between the ECU and the power relay
• Internal ECU fault

How to Fix

1. Read OBD-II codes and record all errors
2. Locate the ECU power relay according to the electrical diagram
3. Check the power and ground of the power relay with a multimeter
4. Check the control signal on the relay coil from the ECU
5. Check the relay itself (replace with a known good one)
6. Inspect and, if necessary, repair the wiring; replace the ECU if it is confirmed to be faulty

Related codes

Error P0685 by Vehicle Brand