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ElectricalSeverity High: diagnose before driving on

P0685ECM/PCM Power Relay Control Circuit/Open

What it means

The ECU sees an open circuit in the control of its own main power relay.

Symptoms

  • No start or stalling
  • ECU not powering up or not shutting down

Common causes

  • Faulty main relay
  • Open control wire
  • Corroded relay socket

What to check first

  1. Check the main relay and its socket
  2. Check the relay control from the ECU
  3. Check ECU supply pins
Can I drive with P0685? Not recommended. P0685 can lead to stalling, limp mode or engine damage; diagnose it before driving further.

Generic OBD-II meaning. Manufacturer-specific meanings and checks can differ; always check the service information for the car.

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P0685: questions and answers

What does P0685 mean?

P0685: ECM/PCM Power Relay Control Circuit/Open. The ECU sees an open circuit in the control of its own main power relay.

What are the symptoms of P0685?

No start or stalling. ECU not powering up or not shutting down.

What causes P0685?

Faulty main relay. Open control wire. Corroded relay socket.

How do you diagnose P0685?

1. Check the main relay and its socket 2. Check the relay control from the ECU 3. Check ECU supply pins

Can I drive with P0685?

Not recommended. P0685 can lead to stalling, limp mode or engine damage; diagnose it before driving further.