P0683
Glow Plug Control Module to PCM Communication CircuitP0683 is a generic OBD-II powertrain diagnostic trouble code: Glow Plug Control Module to PCM Communication Circuit. It is logged by the engine control unit when the glow monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0683 means
P0683 is a diesel-only code. Diesel engines use glow plugs to preheat the combustion chambers for cold starting and to keep combustion stable for a period after the engine fires. The high currents involved are not switched by the engine control module directly but by a separate glow plug control module, which the ECM or PCM commands and then queries for status. The link between the two is a dedicated communication line, either a serial or pulse-width feedback wire or a shared vehicle data bus, depending on the manufacturer.
P0683 sets when the engine control module asks the glow plug control module for a response and either gets nothing back, or gets replies that are corrupted or outside the expected protocol, for a calibrated length of time. The code is about the conversation between the two modules, not about the glow plugs themselves, although a shorted glow plug can drive the control module into self-protection and cause it to stop responding.
The practical consequence is that the engine control module can no longer confirm that preheating is happening. Depending on the strategy it may disable glow plug operation entirely and fall back on a default start. On a cold engine that means extended cranking, a rough first minute, misfire and white or grey smoke while the cylinders come up to temperature. In warm weather the engine may start and run normally with only the warning lamp as evidence.
Common causes
Most-frequently reported root causes when P0683 is logged.
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1
Corroded, loose or damaged connector terminals at the glow plug control module.
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2
Open, chafed or shorted wiring in the communication line between the glow plug module and the engine control module.
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3
Blown fuse or a lost power or ground feed to the glow plug control module.
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4
Internal failure of the glow plug control module, commonly from underhood water and heat exposure.
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5
Weak battery or charging system letting voltage sag far enough during cranking to drop the module offline.
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6
A shorted or excessively low-resistance glow plug overloading the module and forcing it into protection mode.
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7
A poor-quality aftermarket or wrongly specified replacement glow plug control module.
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8
A failed engine control module or out-of-date module software, which is uncommon and should be checked last.
Symptoms drivers notice
How to diagnose P0683
A typical diagnostic flow when this code is present.
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1
Read all stored codes and freeze-frame data, and record every glow plug or module related code that accompanies P0683.
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2
Load-test the battery and check charging system output, since low cranking voltage alone can knock the glow plug module offline.
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3
Inspect the glow plug control module and its connectors for corrosion, water intrusion, melted or backed-out pins and chafed harness sections.
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4
Confirm the module has a good switched power feed and a clean ground with the key on, and check the fuses that supply it.
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5
Check the communication line between the glow plug module and the engine control module for continuity and for shorts to power or ground, flexing the harness to expose intermittent breaks.
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6
With a scan tool, command a glow plug cycle and watch whether the engine control module receives any status back from the glow plug module.
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7
Measure each glow plug for a short or abnormally low resistance that could be forcing the module into protection, before condemning either module.
Related powertrain codes
Frequently asked questions
Can I keep driving with P0683?
In mild weather, usually yes, because glow plugs are mainly needed for cold starting. In cold weather you may find the engine very hard to start, and the extended cranking that follows is hard on the starter and battery, so get it fixed before winter.
Does this mean my glow plugs are bad?
Not necessarily. The code is about lost communication with the glow plug control module. That said, a shorted glow plug can overload the module and make it stop responding, so the plugs should still be tested as part of the diagnosis.
Will it fail an emissions or roadworthiness test?
Yes, if the check engine lamp is on. On top of that, the white smoke and incomplete combustion during a cold start can push the vehicle over an opacity limit if it is tested from cold.
Is this expensive to fix?
It depends on the cause. A corroded connector, a blown fuse or a broken wire is inexpensive. Replacing the glow plug control module costs more, and on some engines the module is mounted in an awkward spot that adds labour time.
Disabling P0683 in software
RaceTune can permanently disable P0683 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
ECU families we can disable P0683 on
We hold the DaVinci A2L disable definitions for these families, so the exact P0683 path and mask addresses are mapped. verified marks a confirmed disable definition. We support many more — upload your file and our identifier will match it automatically.
- Bosch EDC17CP44 verified
- Bosch MD1CP004 verified
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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