OBD Guide
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P0684

Glow Plug Control Module 1 to PCM Communication Circuit Range/Performance

P0684 is an OBD-II diagnostic trouble code meaning: Glow Plug Control Module 1 to PCM Communication Circuit Range/Performance. Common causes: interference or unstable voltage in the gpcm-ecu communication circuit, damage or partial break in data bus wiring. Estimated repair cost: $22–278.

Severity
🔴 High
Can you drive?
Do not drive — repair immediately
Approx. repair cost
$22–278 (est.)

Symptoms

  • Unstable operation of the glow plug system
  • Check Engine Light
  • Unpredictable problems with starting a diesel engine in cold weather
  • The glow plug indicator is on
  • Incorrect GPCM data in diagnostic scanner

Causes

  • Interference or unstable voltage in the GPCM-ECU communication circuit
  • Damage or partial break in data bus wiring
  • GPCM module malfunction (initial stage)
  • Unstable power supply or weight of one of the modules
  • ECU malfunction

How to Fix

  1. Read OBD-II codes and record all errors
  2. Check the power and ground of the GPCM module (normal: 12-14 V when the engine is running)
  3. Inspect the communication circuit wiring for damage, oxidation, breaks
  4. Check the communication circuit with an oscilloscope for interference and signal correctness
  5. Check the GPCM and ECU connectors for oxidation and reliable contact
  6. Replace the GPCM or ECU if they are confirmed to be faulty

Related codes

P0683P0670P0671P0672

Error P0684 by Vehicle Brand

AcuraAudiBAICBMWBYDBuickCadillacChanganCheryChevroletChryslerCitroenDodgeDongfengExeedFAWFordForthingFotonGACGMGMCGeelyGreat WallHavalHondaHongqiHyundaiInfinitiJACJaecooJaguarJeepJetourKaiyiKiaLadaLexusLi AutoLifanLincolnLivanMazdaMercedes-BenzMercuryMitsubishiNIONissanOldsmobileOmodaOpelPeugeotPlymouthPontiacRenaultSWMSaturnSkodaSkywellSubaruSuzukiTankToyotaVolkswagenVolvoVoyahXPengZeekrZotye

FAQ

What does the P0684 code mean?

P0684 is an OBD-II diagnostic trouble code that indicates: Glow Plug Control Module 1 to PCM Communication Circuit Range/Performance

What causes a P0684 error code?

The most common causes of P0684 include: Interference or unstable voltage in the GPCM-ECU communication circuit; Damage or partial break in data bus wiring; GPCM module malfunction (initial stage); Unstable power supply or weight of one of the modules.

How do I fix a P0684 diagnostic trouble code?

To fix P0684: Read OBD-II codes and record all errors. Check the power and ground of the GPCM module (normal: 12-14 V when the engine is running). Inspect the communication circuit wiring for damage, oxidation, breaks. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with P0684?

Do not drive — repair immediately

How much does it cost to fix P0684?

The estimated repair cost for P0684 is $22–278. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat