P0683 — Glow Plug Control Module to PCM Communication Circuit — 6.0 Power Stroke

Diagnostic reference for 6.0 Power Stroke (2003.5–2007) P0683.

Updated October 15, 2026

What it means

The PCM has detected a fault in the diagnostic communication line from the glow plug control module. On the 6.0L this is often a corroded or water-damaged GPCM connector or a failed GPCM, sometimes alongside per-cylinder glow plug codes.¹

Most likely causes

1. Corroded or water-damaged GPCM connector on the frame rail — The GPCM is frame-mounted and exposed to road spray; connector pins can corrode or the housing can allow water ingress, interrupting the diagnostic communication line to the PCM.¹²
2. Failed glow plug control module (GPCM) — Internal failure of the GPCM can break the diagnostic communication link to the PCM while still powering glow plugs intermittently.¹
3. PCM-to-GPCM wiring fault — Chafed, pinched, or open wiring between the PCM and GPCM interrupts the diagnostic communication circuit.²
4. GPCM power or ground supply issue — Loss of proper power/ground to the GPCM can cause communication loss; the PCM may still see the module but cannot complete diagnostics.²
5. Accompanying per-cylinder glow plug circuit faults — P0671–P0678 codes may appear with P0683 when the GPCM detects open or failed glow plugs or under-valve-cover harness faults.¹³

How to diagnose

1. Verify code presence and freeze-frame conditions; confirm P0683 is current and note any accompanying P0671–P0678 codes.
2. Inspect the frame-mounted GPCM connector for corrosion, moisture, bent pins, or damaged seals; look for signs of water intrusion or road-salt buildup.
3. Check GPCM power and ground supplies for proper voltage and continuity per service information; verify no high resistance or intermittent opens.
4. Examine the PCM-to-GPCM wiring harness for chafing, pinching, or damage along the frame rail and engine bay routing; perform a visual and wiggle test while monitoring communication status.
5. Use a scan tool to view GPCM communication/data-pid availability; loss of module response points to GPCM or wiring fault rather than PCM internal failure.
6. If the connector and wiring test good, evaluate GPCM functionality by checking for response to PCM commands and comparing with a known-good module reference; replace only after confirming wiring integrity.

Specs and test values

Common mistake to avoid

Replacing glow plugs or the glow module before checking the batteries. The glow system draws heavily, and low battery voltage causes circuit faults that no part swap will fix. Source: FleetRabbit — P0670 glow plug control module fault.

Parts and tools you may need

• Digital multimeter
• Scan tool with Ford enhanced diagnostics
• Trim removal tools
• Dielectric grease
• Contact cleaner
• Wiring diagram for 6.0 Power Stroke GPCM circuit

Tools you’ll need

• digital multimeter — Checks GPCM power, ground, and wiring continuity to find corrosion or opens causing the PCM-to-GPCM communication fault.
• OBD-II scan tool — Confirms P0683 is current, reads freeze-frame, and monitors GPCM communication/data-pid availability for module response.
• inspection mirror — Lets you see the frame-mounted GPCM connector and harness routing for corrosion, moisture, and damage in tight under-vehicle areas.
• terminal cleaning kit — Cleans corroded or water-damaged GPCM connector pins and seals to restore reliable PCM-to-GPCM diagnostic communication.

Rough cost and difficulty

Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.

When to see a pro

Have a qualified diesel technician confirm the diagnosis and handle any glow plug control module replacement or harness repair. If the truck also has hard cold starts or white smoke at start-up, the glow plugs may not be heating, so get it checked before cold weather.

Check for recalls

Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.

Sources