P0672 on GMC: How to Diagnose & Fix
Cylinder 2 Glow Plug Circuit
1 GMC model · 1 documented issue · $250-$1,200 repair
P0672 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)
P0672 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 P0672 mean on a GMC?
P0672 stands for "Cylinder 2 Glow Plug Circuit." P0672 is a diesel-engine code indicating a fault in the glow plug circuit for cylinder number 2. Glow plugs heat the combustion chamber to help a diesel engine start, especially in cold weather, and the control module monitors each plug's circuit electrically. When it detects an open, short, or out-of-range condition on the cylinder 2 glow plug circuit, it sets this code. It generally causes hard cold starts, rough running until warm, and possibly white smoke on startup, while the check engine or glow plug light may illuminate. On GMC it is documented across 1 model: Sierra 3500HD.
What are the most common causes of P0672?
The most common causes of P0672 are: Failed (open or shorted) glow plug on cylinder 2, Corroded or loose glow plug connector/terminal, Damaged or broken glow plug wiring/harness, Faulty glow plug control module or relay, High resistance/corrosion at the glow plug bus bar or strap, Poor ground connection in the glow plug circuit, Blown fuse feeding the glow plug circuit. The specific cause varies by vehicle.
How much does it cost to fix P0672 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.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.