Cylinder 4 Glow Plug Circuit
The P0674 code means the vehicle's onboard diagnostic system has detected: Cylinder 4 Glow Plug Circuit. This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- moderate
- Estimated cost
- $50 - $500 (parts and labor)
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Common Symptoms
- Check Engine Light on
- Cylinder 4 glow plug not heating
- Reduced system performance
- Warning indicators on dashboard
Probable Causes (Ranked by Likelihood)
- Failed glow plug in Cylinder 4 Very High
- Wiring damage or corrosion in the circuit High
- Poor electrical connection at module or component Moderate
- ECM or control module internal failure Low
Common Fixes by Vehicle
What techs usually find when diagnosing P0674 on specific vehicles — tap your vehicle for the fix and the exact part:
2001-2010 Duramax 6.6L hard DIY
P0674 = Glow Plug #4. Follow standard Duramax glow plug replacement procedure -- all 8 at once, AC Delco or NGK plugs only, 11 ft-lb torque. If P0674 recurs, suspect the GPCM or harness. The harness connector at the valve cover is a common failure point.
Labor: 3-4 hours2003-2007 Ford 6.0L Power Stroke hard DIY
6.0L P0674 = glow plug #4. If only P0674 is showing and no other glow plug codes, it's likely a single failed plug or harness pigtail. Do the whole set anyway -- Motorcraft x8 -- because the others are close behind. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 4-6 hours2008-2010 Ford 6.4L Power Stroke hard DIY
6.4L P0674 = glow plug #4. On 6.4L, confirm GPCM is functional (check for voltage on each plug lead during crank with a test light) before buying plugs -- a bad GPCM can fake multiple plug codes.
Labor: 6-10 hoursFrequently Asked Questions
What happens when Cylinder 4 glow plug fails?
A single failed glow plug in Cylinder 4 may cause hard starting in cold weather and rough running until the engine warms up. In mild temperatures, you may not notice any symptoms. Multiple failed glow plugs cause progressively worse cold starting.
How much does a glow plug replacement cost?
Individual glow plugs cost $15 to $50 each. Labor is the main expense as some glow plugs are difficult to access. A single glow plug replacement typically costs $100 to $300. Many shops recommend replacing all glow plugs at once.
Can a glow plug break off during removal?
Yes, especially on high-mileage diesel engines. Carbon buildup and corrosion can seize the glow plug in the cylinder head. Special extraction tools exist for broken glow plugs. Applying penetrating oil days before removal helps.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
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Use a scan tool to read data related to Cylinder 4 Glow Plug
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Inspect all related wiring, connectors, and grounds for damage, corrosion, or loose connections
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Measure circuit voltage, resistance, and continuity to identify the fault type
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Check for technical service bulletins related to this code for your specific vehicle
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
P0674 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
Commonly Affected Vehicles
- 2008-2018 Ford F-250 6.7L Powerstroke
- 2010-2020 Ram 2500 6.7L Cummins
- 2011-2019 Chevrolet Silverado 6.6L Duramax
- 2012-2020 Volkswagen Jetta TDI
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