P0674 on GMC
Cylinder 4 Glow Plug Circuit
P0674 on GMC vehicles indicates cylinder 4 glow plug circuit. Au7o has documented this code across 1 GMC model — most commonly on Sierra 3500HD. This is a diesel engine code. Glow plugs preheat each cylinder so the diesel fuel ignites reliably, especially during cold starts. P0674 means the glow plug control system detected an electrical fault in the cylinder 4 glow plug circuit — commonly an open circuit, a short, or resistance outside the normal range. The typical symptoms are difficult cold starting, rough running until the engine warms, more startup smoke, and possibly an illuminated glow plug indicator. Typical repair costs on GMC range from $250 to $1,200, depending on the specific model and root cause.
Common Causes of P0674
- •Failed (open or shorted) cylinder 4 glow plug
- •Damaged or corroded glow plug wiring/connector
- •Loose or corroded glow plug terminal/strap
- •Faulty glow plug relay or control module
- •Broken or chafed harness to the glow plug
- •Poor ground or low supply voltage to the circuit
P0674 on GMC by Model
GMC Sierra 3500HD(1 issue)
- Glow plug control module / glow plug circuit faults causing hard cold starts (Duramax)2007-2019
Duramax-equipped Sierra 3500HD owners report hard starting, extended cranking, and rough idle in cold weather due to glow plug system faults. NHTSA complaints and service information commonly involve failed glow plugs, glow plug control module issues, or wiring/connector problems that trigger circuit DTCs and reduce preheat performance.
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View P0674 across all makes →Frequently Asked Questions
What does P0674 mean on GMC?▼
P0674 stands for "Cylinder 4 Glow Plug Circuit." This is a diesel engine code. Glow plugs preheat each cylinder so the diesel fuel ignites reliably, especially during cold starts. P0674 means the glow plug control system detected an electrical fault in the cylinder 4 glow plug circuit — commonly an open circuit, a short, or resistance outside the normal range. The typical symptoms are difficult cold starting, rough running until the engine warms, more startup smoke, and possibly an illuminated glow plug indicator. On GMC specifically, this code is documented across 1 model.
What causes P0674 on GMC vehicles?▼
Common causes on GMC: Failed (open or shorted) cylinder 4 glow plug, Damaged or corroded glow plug wiring/connector, Loose or corroded glow plug terminal/strap, Faulty glow plug relay or control module, Broken or chafed harness to the glow plug. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0674 on a GMC?▼
Repair costs on GMC range from $250 to $1,200, depending on the specific model and root cause.
Which GMC models have P0674 documented?▼
Au7o has documented P0674 on 1 GMC model: Sierra 3500HD.