OBD Guide
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P0685

ECM/PCM Power Relay Control Circuit/Open

P0685 is an OBD-II diagnostic trouble code meaning: ECM/PCM Power Relay Control Circuit/Open. Common causes: open circuit control circuit of the ecu power relay coil, ecu power relay malfunction. Estimated repair cost: $6–889.

Severity
🚨 Critical
Can you drive?
Do not drive — repair immediately
Approx. repair cost
$6–889 (est.)

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

P0686P0687P0688P0689P0690

Error P0685 by Vehicle Brand

AcuraAudiBAICBMWBYDBuickCadillacChanganCheryChevroletChryslerCitroenDodgeDongfengExeedFAWFordForthingFotonGACGMGMCGeelyGreat WallHavalHondaHongqiHyundaiInfinitiJACJaecooJaguarJeepJetourKaiyiKiaLadaLexusLi AutoLifanLincolnLivanMazdaMercedes-BenzMercuryMitsubishiNIONissanOldsmobileOmodaOpelPeugeotPlymouthPontiacRenaultSWMSaturnSkodaSkywellSubaruSuzukiTankToyotaVolkswagenVolvoVoyahXPengZeekrZotye

FAQ

What does the P0685 code mean?

P0685 is an OBD-II diagnostic trouble code that indicates: ECM/PCM Power Relay Control Circuit/Open

What causes a P0685 error code?

The most common causes of P0685 include: 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.

How do I fix a P0685 diagnostic trouble code?

To fix P0685: Read OBD-II codes and record all errors. Locate the ECU power relay according to the electrical diagram. Check the power and ground of the power relay with a multimeter. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with P0685?

Do not drive — repair immediately

How much does it cost to fix P0685?

The estimated repair cost for P0685 is $6–889. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat