P0674
UniversalCylinder 4 Glow Plug Circuit/Open
Medium SeverityThis code indicates a problem with the electrical circuit for the glow plug in cylinder 4. A malfunctioning glow plug primarily impacts a diesel engine's ability to start smoothly in cold weather and can affect emissions.
⚠️ Before You Begin (Safety First)
Always ensure the engine is cool before working on glow plugs to prevent burns. Disconnect the battery before performing any electrical work to avoid accidental short circuits or electrical shocks. Use appropriate eye protection.
Common Symptoms
- Hard starting in cold weather
- Check Engine Light (CEL) illumination
- Rough idling immediately after a cold start
- Reduced engine performance (less common but possible)
- Increased exhaust smoke during cold starts
Common Causes
- Failed glow plug in cylinder 4
- Open or short circuit in the glow plug wiring
- Faulty Glow Plug Control Module (GPCM)
- Corroded or loose electrical connections to the glow plug or GPCM
Frequently reported on: Ford F-250 Diesel (2011-2016), Ram 2500 Diesel (2010-2015), Chevrolet Silverado 2500HD Duramax (2007-2013), Volkswagen Jetta TDI (2006-2010)
Diagnostic Steps
- Gather necessary tools: multimeter, glow plug socket set, torque wrench, dielectric grease, anti-seize compound.
- Locate cylinder 4's glow plug (consult your vehicle's repair manual for exact location).
- Disconnect the battery.
- Carefully disconnect the electrical connector from the glow plug.
- Test the glow plug's resistance with a multimeter. A reading outside the manufacturer's specification (typically 0.6-2.0 ohms) indicates a faulty glow plug. You can also test for continuity to ground.
- If faulty, carefully remove the glow plug using a glow plug socket. Be gentle to avoid breaking it off in the cylinder head.
- Apply anti-seize to the threads of the new glow plug and install it, torquing to manufacturer specifications.
- Reconnect the electrical connector and the battery. Clear the code and test the vehicle.
👨🔧 When to Call a Professional
If the glow plug is seized in the cylinder head, or if diagnostic testing indicates a failure of the Glow Plug Control Module, it is best to consult a professional technician to avoid costly damage to the cylinder head during removal.
Commonly Asked Questions
What is a glow plug and why is it important?
A glow plug is an electrical heating device used in diesel engines to aid in starting in cold weather. It preheats the combustion chamber, allowing the diesel fuel to ignite more easily and ensuring smoother cold starts.
Can I drive my car with a P0674 code?
While you can usually drive with a single faulty glow plug, it may result in hard starting, especially in cold conditions, and slightly increased emissions. It's recommended to address it promptly to avoid further issues or more difficult starting.
Is replacing a glow plug a difficult DIY repair?
It can be a moderately difficult DIY repair. Access to the glow plugs can be challenging on some engines, and there's a risk of breaking the glow plug off in the cylinder head if not removed carefully. Always use a proper glow plug socket and torque wrench.
What are the common causes for a P0674 code?
The most common causes are a failed glow plug itself, an open circuit or damaged wiring to the glow plug, or a malfunctioning glow plug control module (GPCM) that supplies power to the glow plugs.
How do I test the glow plug to confirm it's faulty?
You can test a glow plug using a multimeter. Disconnect its electrical connector and measure the resistance across its terminals. Compare the reading to your vehicle's specifications. An open circuit (infinite resistance) or a reading far outside the specified range indicates a faulty glow plug. You can also check for continuity to the engine block.