Individual glow plug failure on the 6.7L Power Stroke shows up as hard cold-starts, P067X codes for specific cylinders, and extended cranking in winter. Here's when to replace one versus the full set and what each scope runs.
What this issue is
Individual glow plug failure on the 6.7L Power Stroke shows up as cold-start problems and P067X codes pointing at specific cylinders. Unlike the P0670 code (which points at the glow plug control module), the P0671 through P0678 codes each identify a specific failed glow plug — P0671 is cylinder 1, P0672 is cylinder 2, and so on through P0678 for cylinder 8.
Glow plug failures are among the most common cold-weather complaints we see on the 6.7L. The symptom pattern is distinctive — warm starts work fine; cold starts get progressively harder as ambient temperatures drop. Most owners first notice the issue the first cold morning of the season, and by the time they’re in the shop it’s usually because the truck has gotten to the point of extended cranking or no-start.
The repair itself isn’t dramatic, but the conversation about scope matters — replace the one failed plug, or replace the set while we’re in there.
Symptoms you’ll notice
- Check Engine Light with P067X codes for one or more specific cylinders (P0671 through P0678)
- Hard cold-start — truck takes noticeably longer to fire in cool or cold weather
- Extended cranking — what should take 2-3 seconds takes 8-15 seconds or more on cold mornings
- Rough idle for the first minute after a cold start as the affected cylinder takes longer to join in cleanly
- White or gray smoke on cold start, clearing as the engine warms — the affected cylinder is pumping uncombusted or partially-combusted fuel
- Noticeable cylinder miss under 40 degrees F, smoothing out once the engine reaches operating temperature
- Progressively worse starting as outside temperatures drop — a plug that’s borderline in 45-degree weather becomes unable to fire its cylinder at 20 degrees
- Fine in summer, bad in winter — the most distinctive symptom and often the first sign
The temperature dependence is the giveaway. A mechanical problem affects starts in all weather; glow plug issues only show up when glow plugs are needed.
Why it happens
1. Normal wear. Glow plugs are heating elements operating in a hot, pressurized combustion chamber. The filament wears over time, resistance changes, and eventually the plug can no longer generate enough heat to assist cold-start. This is by far the most common cause.
2. Electrical issues on individual circuits. Connector corrosion or damaged wiring at specific cylinders can cause an individual glow plug circuit to fail even when the plug itself is still healthy. Diagnostic distinguishes the two.
3. Contamination or carbon buildup. Severe carbon buildup on the plug tip can insulate it and reduce its ability to heat the combustion chamber. Less common, but possible on very high mileage or poorly-maintained trucks.
4. Module fault affecting individual cylinders. Sometimes a GPCM failure presents as codes on specific cylinders rather than the system-wide P0670 — see our P0670 article for that scenario.
5. Quality issues with aftermarket plugs. Trucks that had aftermarket glow plugs installed previously sometimes see early failures from the aftermarket parts themselves. We use OEM Motorcraft glow plugs for reliability — the quality difference isn’t worth the early-failure risk.
How we diagnose it
Sequence:
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Pull all stored codes. P067X codes point directly at individual cylinders. P0670 alongside indicates a module issue also present.
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Resistance test each glow plug. With the glow plugs accessed, measure resistance across each. Healthy plugs read close to each other; a plug reading significantly different (open circuit, short, or out-of-spec high resistance) is failed.
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Connector and harness inspection. Check the connector at each glow plug for corrosion or damage. Wiring inspection confirms whether the issue is plug-side or circuit-side.
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Functional test with scan tool. Command the glow plug system on through the factory scan tool and monitor the module’s report back. Patterns in the data confirm which plugs are failing and whether the module is reporting accurately.
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Set-condition review. Check the age and mileage of the existing glow plug set. That data shapes the recommendation — replace one plug, replace the set, or replace plus address the module.
By the end we know exactly which plugs are failed, whether the module is healthy, and what the right scope is.
What the repair looks like
Individual glow plug replacement. The affected plug is unthreaded from the cylinder head and replaced with OEM Motorcraft. Access requires removal of some upper engine components (valve covers on some model years, intake components on others) but isn’t a major teardown.
Full set replacement (all 8 plugs). Same access labor as a single plug — once we’re in there, replacing all 8 is a parts work addition rather than a major labor increase. This is usually the right call on higher-mileage trucks.
Module plus glow plug service. When the P0670 code is present alongside P067X codes, both need addressing. See our P0670 Glow Plug Module article for that combined scope.
Wiring or connector repair. When diagnostic identifies harness damage rather than plug failure, repair is specific to what’s damaged.
Pricing
Final pricing depends on labor, parts, and diagnostic findings — we walk through every line item with you before work begins. Call the shop or request an estimate with your year, mileage, and symptoms for a quote on your specific situation.