P0670 — Glow Plug Control Module Control Circuit — 6.0 Power Stroke

The PCM has detected a fault in the circuit it uses to command the glow plug control module on a 6.0L Power Stroke. The GPCM is frame-mounted and drives the…

Updated October 15, 2026

What it means

Generic definition: The PCM has detected a fault in the circuit it uses to command the glow plug control module. Platform note: On the 6.0L the GPCM is frame-mounted and reports per-cylinder glow plug faults P0671–P0678 and its own communication fault P0683.¹²

Most likely causes

1. GPCM connector corrosion or water intrusion on the frame rail — The GPCM sits on the frame rail where moisture and road salt collect; corrosion or water damage at the connector can interrupt the PCM-to-GPCM command circuit.¹²
2. GPCM power or ground supply fault — Loss of battery voltage or a poor ground to the GPCM prevents the module from receiving the PCM command and operating the glow plugs.¹
3. PCM-to-GPCM wiring open/short or chafing — Wiring between the PCM and the GPCM can chafe or be damaged, producing an open or short in the control circuit.¹
4. Failed glow plug control module — Internal failure of the GPCM can cause the PCM to detect a control-circuit fault even when wiring and power are good.²
5. Related per-cylinder glow plug circuit faults — Individual glow plug opens or harness faults can contribute to overall glow system issues and may appear alongside P0670.³⁴

How to diagnose

1. Verify the code and freeze-frame data; confirm cold-start symptoms and check for accompanying P0671–P0678 or P0683.
2. Inspect the frame-mounted GPCM connector for corrosion, moisture, or damaged pins; clean/dry as needed and check connector seating.
3. Check GPCM power and ground feeds for proper voltage and continuity; repair any high resistance or open circuits.
4. Inspect PCM-to-GPCM wiring harness for chafing, opens, or shorts, especially where the harness routes near the frame or transmission area.
5. Using a scan tool, monitor GPCM communication and command status; if communication is lost or erratic, suspect GPCM or wiring.
6. If wiring and power are good but the control-circuit fault persists, evaluate the GPCM for internal failure.

Specs and test values

Common mistake to avoid

Condemning the FICM or injectors before checking the batteries. The FICM needs good battery voltage to hold its output; weak batteries or a poor charging system can drag it below spec and look like a module failure. Source: DieselHub — 6.0 Power Stroke FICM troubleshooting.

Parts and tools you may need

• Digital multimeter
• Scan tool with Ford enhanced diagnostics
• Contact cleaner and dielectric grease
• Basic hand tools for connector access

Tools you’ll need

• OBD-II scan tool — Reads P0670 and related P0671–P0678/P0683 codes and monitors GPCM communication/command status for this 6.0L Power Stroke diagnosis.
• digital multimeter — Checks GPCM power/ground supply voltage and continuity and tests PCM-to-GPCM wiring for opens/shorts or high resistance.
• inspection mirror — Lets you see the frame-mounted GPCM connector and harness routing in tight areas for corrosion, moisture, or chafing.
• electrical contact cleaner — Cleans corrosion/moisture from the GPCM connector pins to restore reliable PCM-to-GPCM circuit integrity.

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

If wiring repairs are needed in tight or safety-critical areas, or if the GPCM requires replacement and programming verification, have a qualified diesel technician perform the work.

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