P0671 on the 6.0L Power Stroke is a glow plug cylinder 1 circuit fault. The 6.0L uses glow plugs to preheat each cylinder for cold starting, and the glow plug control module monitors each plug's circuit individually. P0671 sets when the module detects a fault on the cylinder 1 glow plug circuit, meaning that plug is drawing too little or too much current, or the circuit to it is open or shorted.
Because the code names a single cylinder, it points you directly at the cylinder 1 glow plug and its feed. On the 6.0L the glow plugs live under the valve covers and are fed through the valve cover harness, so a single-cylinder fault often traces to a burned-out plug or a damaged harness connection rather than the control module. Confirming the plug and its circuit first keeps the repair focused and inexpensive.
What P0671 means
The glow plug control module energizes each glow plug and monitors current draw. P0671 sets when the cylinder 1 circuit is outside the expected range, indicating an open glow plug, a shorted plug, or a break or short in the wiring to that cylinder. It is a per-cylinder circuit code that isolates the fault to the cylinder 1 glow plug and its feed.
Common causes
- Burned-out or open cylinder 1 glow plug
- Damaged valve cover harness feeding cylinder 1
- Corroded or loose glow plug connector
- Shorted glow plug drawing excess current
- Wiring open or shorted between the module and cylinder 1
Symptoms
- Hard cold starting and extended cranking
- White smoke and rough running when cold
- Check engine light with P0671 stored
- A single cylinder slow to fire on a cold start
- Little change once the engine is warm
How to diagnose it
Access the cylinder 1 glow plug and measure its resistance; a good plug reads a low resistance, while an open plug reads very high. Inspect the valve cover harness and the glow plug connector for corrosion, oil, and damage. Check the wiring from the glow plug control module to cylinder 1 for an open or a short. Compare cylinder 1 to a known-good cylinder to confirm the fault is isolated to that plug and circuit rather than a module-wide issue.
How to fix it
Replace the cylinder 1 glow plug if it reads open or shorted, and repair or replace a damaged valve cover harness or corroded connector. If the plug and wiring are good but the fault persists, test the glow plug control module. After the repair, clear the code, confirm all glow plug circuits pass, and verify a clean cold start. For glow plugs, valve cover harnesses, and glow plug control modules for your 6.0L Power Stroke, contact sales@coredieselparts.com.
Frequently asked questions
Can I drive with P0671?
Once warm the engine runs normally, but cold starts suffer. A single weak glow plug means harder starting, white smoke, and rough running until warm, so repair it before cold weather.
Is P0671 the glow plug or the module?
Because it names one cylinder, start with that glow plug and its wiring. A module fault usually affects multiple circuits, so an isolated cylinder 1 code points at the plug or its feed first.
Should I replace all glow plugs at once?
If the others are original and high mileage, replacing the full set while you are in there is reasonable, since they tend to wear at similar rates and prevents repeat repairs.
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