P0674: Cylinder 4 Glow Plug Circuit
Severity: medium
What it means: The engine computer sees an open or faulty circuit for the cylinder 4 glow plug. The glow plug heats that cylinder so a diesel starts easily when cold.
Safe to drive? Yes, usually. The engine may be hard to start when cold and may smoke at startup, but glow plugs don't affect driving once it's running.
Common symptoms
- Hard starting or rough running right after a cold start
- White smoke at cold startup
- Check engine light
Likely causes, ranked
- Failed cylinder 4 glow plugDIY
- Failed glow plug control moduleDIY
- Damaged wiring or connector at the plugDIY
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Vehicle-specific notes
- 2003–2018 Freightliner Sprinter: A 2006 Freightliner Sprinter owner had P0674 and P0673 with P0380 on cold starts. Owners said to replace the plugs, and the controller if codes came back. Read the full answer · Source
DIY or shop?
DIY for careful owners. Use low torque and go slowly, because glow plugs can snap. A snapped plug is a shop job.
Before you replace parts
- Read all stored codes and note which cylinders are listed.
- Check the glow plug connectors and wiring for damage or corrosion.
- Test the glow plug's resistance before replacing it.
- If codes for several cylinders show up or keep moving, test the glow plug control module.
- Clear the codes after the repair and confirm they stay off on the next cold start.
Safety / mechanic note
Verify with a mechanic. A code points to a system, not always a specific part.
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