Error code

OBD2 P0685

OBD2P0685
Diagnostic Trouble Code· Standard OBD-II fault code read from the vehicle's onboard diagnostics.

What it means

ECM/PCM Power Relay Control Circuit /Open.

Severity

highNot drivable in some cases due to no-start/no-crank condition.

Summary

P0685 indicates an issue with the ECM/PCM power relay control circuit being open or disconnected, affecting the power supply to the engine control module.

Symptoms

  • Stored trouble code and possibly an illuminated warning light
  • No-start or no-crank condition
  • Engine may start but run poorly

Common Causes

  • Defective PCM power-supply relay
  • Low system voltage
  • Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
  • Defective ignition switch
  • Failed or failing PCM or other control module (rare)

Diagnosis

  1. Record all fault codes and freeze frame data.
  2. Locate the PCM power relay and refer to manual for terminal configuration.
  3. Perform a thorough visual inspection of wiring and connectors.
  4. Test for voltage at primary and secondary terminals on the relay.
  5. Check system voltage at the PCM connector.
  6. Remove and test the relay as per instructions in the manual.
  7. Suspect programming error or defect in the PCM if all electrical values check out.

Fixes

  • Replace defective PCM power-supply relay

FAQ

What should I do if my car won't start and P0685 is present?

Check the wiring, connectors, and ignition switch. If these are fine, replace the PCM power-supply relay.

Can a low battery cause this code to appear?

Yes, low system voltage can trigger P0685 as it affects the power supply to the ECM/PCM.

View source

Not affiliated with OBD2. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.

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