What Does P0683 Mean?
The PCM has detected a fault in the communication circuit between the glow plug control module (GPCM) and the PCM. This is a data link issue rather than a glow plug hardware problem. The PCM cannot receive glow plug status information from the GPCM, which may prevent proper glow plug activation timing. The driver may notice the glow plug wait light not illuminating or behaving erratically, along with hard cold starts.
Common Causes
30%
Faulty wiring in the communication bus between GPCM and PCM
30%
Failed glow plug control module (communication circuit failure)
20%
Corroded or loose connector at GPCM or PCM communication pins
10%
PCM communication port fault
10%
Electromagnetic interference affecting the communication line
Diagnostic Steps
1
Check for additional CAN bus communication codes; if present, the issue may be a broader network fault rather than specific to the GPCM.
2
Inspect the connector at the GPCM for bent, corroded, or backed-out pins on the communication circuit terminals (refer to wiring diagram for pin identification).
3
Measure the resistance of the communication wires between the GPCM and PCM connectors with both modules disconnected; continuity should be present with no shorts between wires or to ground.
4
Using an oscilloscope, monitor the communication line for proper signal patterns during key-on; a flat line or distorted signal indicates a hardware fault on one end.
5
Verify GPCM power and ground circuits are within spec, as low voltage supply can cause communication failures even if the comm circuit itself is intact.
6
If all wiring tests pass, substitute a known-good GPCM to determine if the module or PCM is the root cause.
Estimated Repair Cost
$150 - $800
Parts + labor, varies by vehicle and location
The PCM has detected a fault in the communication circuit between the glow plug control module (GPCM) and the PCM. This is a data link issue rather than a glow plug hardware problem. The PCM cannot receive glow plug status information from the GPCM, which may prevent proper glow plug activation timi...
The most common cause of P0683 (Glow Plug Control Module to PCM Communication Circuit) is: Faulty wiring in the communication bus between GPCM and PCM
Typical repair costs for P0683 range from $150 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive once the engine is running. Without proper PCM-to-GPCM communication, glow plug activation may default to a fixed strategy or not activate at all, making cold starts unreliable. In extreme cold, the engine may fail to start entirely.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0683 to identify the root cause.
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Quick Info
Category
Powertrain
System
Diesel Cold Start / Glow Plug System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
