P0674 on GMC: How to Diagnose & Fix
Cylinder 4 Glow Plug Circuit
1 GMC model · 1 documented issue · $250-$1,200 repair
P0674 on GMC by model: symptoms, diagnosis and fix
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.
Common Symptoms
- Hard start or no-start in cold temperatures
- Extended cranking time
- Rough idle and white/gray smoke on startup
- Check Engine light with glow plug circuit codes
- Reduced power briefly after cold start
How to Fix
Scan for glow plug and control module DTCs, load-test the glow plugs, and inspect harness/connectors at the glow plug controller. Replace failed glow plugs and/or the glow plug control module as indicated, then clear codes and verify proper preheat operation. Use OEM glow plugs specified for the engine (LMM/LML/L5P vary by year).
Sources for this issue (1)
P0674 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0674 mean on a 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 it is documented across 1 model: Sierra 3500HD.
What are the most common causes of P0674?
The most common causes of P0674 are: 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. The specific cause varies by vehicle.
How much does it cost to fix P0674 on a GMC?
Published repair estimates on GMC range from $250 to $1,200 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0674 on a different make?
View P0674 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.