P0684 OBD II Trouble Code GPCM to PCM Communication Circuit Range/Performance

Symptoms of P0684 OBD II Trouble Code

  • The check engine light will be illuminated and the above codes will be set.
  • Little if any indication will be present if only one or two glow plugs have failed. If the engine is very cold it may be a little harder to start.
  • The engine may exhibit a miss until it has sufficiently warmed up.
  • If more than two glow plugs are malfunctioning, the engine will be very difficult to start.

Common Causes of P0684 OBD II Trouble Code

  • Open or short in the wiring from the PCM to the GPCM, to the bus bar, or from the bus bar to the glow plug.
  • Failed glow plug
  • Loose or corroded connections
  • Failed GPCM
  • Loose or corroded connections on the glow plug solenoid
  • Glow plug solenoid failure
  • Insufficient battery power to solenoid
  • Code P0670 may accompany this code. This code points to the wiring harness from the GPCM to the solenoid as a problem.