P0685: ECM/PCM Power Relay Control Circuit/Open
MediumPowertrainEngine Electronics
What does P0685 mean?
P0685 is a diagnostic trouble code indicating "ECM/PCM Power Relay Control Circuit/Open". This means there is an electrical break in the engine electronics wiring — a connector may be unplugged, a wire broken, or a component has failed internally. The ECU detected no signal where it expected one.
Symptoms you may notice
- Check engine light (MIL) illuminated on dashboard
- Intermittent warning lights
- Erratic gauge readings
Estimated repair cost
Typical range in Australia (parts + labour)
$80 – $400 AUD
Common causes
- Damaged or corroded wiring harness
- Loose or disconnected electrical connector
- Failed engine electronics sensor or actuator
- Blown fuse in the related circuit
- Poor ground connection
What should you do?
This code sits in a powertrain control module. The engine or transmission can drop into limp mode or cut out, which is its own hazard in traffic or on a motorway. Get it diagnosed before your next trip rather than waiting for the next service.
Get a diagnosis for YOUR car
Code P0685 can mean different things depending on your vehicle. TorqueBot gives you a diagnosis specific to your make, model, and year.