Code Definition

P0685 — Control Module Power Relay “A” Control Circuit/Open

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Holden

About P0685

P0685 is a generic (obd-ii standard) powertrain diagnostic trouble code recorded for Holden vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0685 is stored, the module has detected an open (broken or disconnected) electrical path in the monitored circuit.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0685 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The engine control module (ECM/PCM) controls its own main power relay, referred to as Power Relay A, to feed the ignition on and run circuits and to keep itself powered for after run functions. The PCM energises the relay coil by switching ground or battery voltage to it, and monitors the control circuit for proper current draw or voltage feedback. DTC P0685 is set when the PCM commands the relay on but detects an open circuit, excessive resistance, or no coil current within its specified timeout, indicating the relay control circuit is open or cannot be controlled. Because this relay feeds th...

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