P0683: Glow Plug Control Module to PCM Communication Circuit (Meaning, Causes, Fixes)
What P0683 means
Diesel engines ignite fuel with the heat of highly compressed air, and glow plugs (small heaters in each cylinder) help a cold engine reach that heat. OBD-Codes.com explains that when the PCM senses a cold engine (from the oil and transmission temperature sensors), it grounds the glow plug control module (GPCM); the module then switches a glow plug solenoid, which sends battery power through a bus bar to each glow plug, and the module acts as a timer so the plugs only run for a few seconds. RepairPal says P0683 sets when the PCM cannot communicate with the glow plug module. OBD-Codes.com describes it as a lost-communication fault that keeps the PCM from sending its essentially on/off command to the module, and notes the code names the area of failure, not a specific part. The two sources agree on the definition but weight the causes differently: RepairPal lists the glow plug control module, the PCM and wiring, while OBD-Codes.com's technician says that in his experience high-current connections and burned-out glow plugs are the usual culprits and the low-current module is the least likely part to fail.
Severity: can I keep driving?
Stop and fix promptly
RepairPal rates P0683 urgent, meaning immediate action is needed. The main risk is not being able to start: RepairPal lists 'engine may not start' and 'hard or no start in cold weather', and OBD-Codes.com says the engine will be very difficult to start if more than two glow plugs aren't working. A warm, running engine usually keeps running, but get it diagnosed before cold weather strands you.
Common symptoms
- Check engine light on (OBD-Codes.com)
- Hard starting, or no start, especially in cold weather (both sources)
- Engine misses until it warms up (OBD-Codes.com)
- Little or no noticeable symptom if only one or two glow plugs have failed; very hard starting if more than two have (OBD-Codes.com)
Likely causes
Roughly most to least common, based on the sources below. Your vehicle may differ.
- Open or short in the wiring from the PCM to the glow plug control module, to the bus bar, or from the bus bar to a glow plug (OBD-Codes.com; RepairPal lists wiring issues)
- Loose or corroded connections, including at the glow plug solenoid (OBD-Codes.com)
- Failed glow plug control module (both sources; OBD-Codes.com calls it the least likely part to fail)
- Failed glow plugs (OBD-Codes.com)
- Failed glow plug solenoid or not enough battery power reaching it (OBD-Codes.com)
- Faulty PCM (RepairPal; OBD-Codes.com's last test step points to the PCM if the module gets no signal)
Diagnostic steps you can do
Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.
- Make sure the batteries are fully charged, since OBD-Codes.com lists insufficient battery power to the solenoid as a cause.
- Visually trace the wiring from the PCM to the glow plug control module, the solenoid (often on the valve cover), the bus bar and each glow plug, looking for loose, burned or corroded connectors. OBD-Codes.com notes that with the high current involved, even slight looseness can arc and burn a connector.
- Unplug the connector at the glow plug control module, check for pushed-out pins and corrosion, check the terminals for a short to ground with an ohmmeter, then reconnect with dielectric grease (OBD-Codes.com).
- Check each glow plug's resistance to ground. OBD-Codes.com's P0683 article gives 0.5 to 2.0 ohms as good, while its P0670 article says under about 0.4 ohms; the right value depends on the engine, so use your service manual's spec.
Typical fixes
- Repair open, shorted, loose or corroded wiring and connectors (both sources)
- Replace failed glow plugs or a bad glow plug-to-bus bar wire (OBD-Codes.com)
- Replace a failed glow plug control module (both sources)
- Replace a failed glow plug solenoid (OBD-Codes.com, which says it is seldom the problem)
- PCM repair or replacement only after everything else is ruled out (RepairPal lists PCM failure as a cause)
Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.
🛠 When to call a pro
- OBD-Codes.com describes using the service manual's glow plug wiring diagram to probe voltage: no signal from the PCM to the module points to the PCM, while signal into the module but no voltage out to the solenoid points to the module
- Checking wiring resistance from each glow plug to the bus bar against the manufacturer's spec
- Checking for related codes such as P0670, which OBD-Codes.com says may accompany P0683
Where to buy
Plain search links. Always match parts to your exact year, make, model and engine.
FAQs
Can I drive with P0683?
If the engine is already running it usually keeps running, but RepairPal rates P0683 urgent because the engine may not start, especially in cold weather. Fix it before you risk being stranded.
Does P0683 happen on gas engines?
No. Glow plugs are a diesel part; both RepairPal and OBD-Codes.com describe the glow plug system as part of a diesel engine.
Is the glow plug module usually the problem?
Not necessarily. RepairPal lists the module, the PCM and wiring as common causes, but OBD-Codes.com's technician says loose or burned high-current connections and failed glow plugs are more common and the module is the least likely to fail. Check the wiring and plugs first.
Sources
Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.