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DTC codes / P06xx · Computer and output circuits / P0683

P0683Glow Plug Control Module to PCM Communication Circuit

P0683 is a generic powertrain code indicating that the powertrain control module (PCM) has detected a communication fault on the circuit linking it to the glow plug control module. The PCM monitors this dedicated serial data line for expected messages and sets the code when the signal is missing, intermittent, or implausible, which can prevent the glow plugs from being commanded on.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms
  • Hard starting or extended cranking when the engine is cold
  • Rough idle or white smoke immediately after a cold start
  • Reduced fuel economy during warm-up
  • In some vehicles, a message indicating glow plug system service required

Common causes, most likely first

  1. Open or shorted communication wire between the glow plug control module and the PCM
  2. Corroded, loose, or damaged connector pins at either module
  3. Failed glow plug control module
  4. Failed powertrain control module (less common)
  5. Poor ground connection shared by the glow plug control module
  6. Electrical interference or chafed wiring harness causing intermittent communication

How to diagnose and fix it

  1. Scan all modules for related codes and record freeze-frame data to understand when the fault occurs
  2. Inspect the communication circuit wiring and connectors between the glow plug control module and PCM for damage or corrosion
  3. Check the glow plug control module's power and ground circuits with a multimeter under load
  4. Perform a voltage drop or resistance test on the communication line to confirm an open or short
  5. If wiring is intact, substitute a known-good glow plug control module and clear the code to see if it returns
  6. Verify the repair by clearing codes and performing a cold-start test cycle

Why the glow plug module often gets replaced unnecessarily

  • A chafed wire or corroded pin is a far more common cause of P0683 than a failed glow plug control module, so always inspect the harness before condemning the module.
  • The code can be set by a momentary loss of communication that leaves no current symptom, so a single occurrence may not justify parts replacement.
  • Some vehicles use a shared ground for the glow plug control module and other components; a bad ground can mimic a communication failure.
  • P0683 does not always mean the glow plugs themselves are faulty; the code specifically points to the communication link, not the glow plug resistance.
  • Aftermarket electrical accessories or poor previous repairs can introduce noise on the communication line and trigger this code intermittently.

Can I keep driving with P0683?

You can generally drive the vehicle, but cold starting may be difficult and prolonged cranking can wear the starter and battery. Avoid relying on the vehicle for cold-weather starts until the fault is repaired, and do not clear the code without diagnosing it first.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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