P0673 on GMC: How to Diagnose & Fix
Cylinder 3 Glow Plug Circuit
1 GMC model · 1 documented issue · $250-$1,200 repair
P0673 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)
P0673 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 P0673 mean on a GMC?
P0673 stands for "Cylinder 3 Glow Plug Circuit." This is a diesel engine code. Glow plugs heat each cylinder's combustion chamber to make starting easier, particularly in cold conditions. P0673 means the glow plug control system detected an electrical problem in the cylinder 3 glow plug circuit — usually an open circuit, a short, or out-of-range resistance. You'll most likely notice harder cold starts, rough idle while warming up, or extra startup smoke; the glow plug warning light may also illuminate. On GMC it is documented across 1 model: Sierra 3500HD.
What are the most common causes of P0673?
The most common causes of P0673 are: Failed (open or shorted) cylinder 3 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 P0673 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 P0673 on a different make?
View P0673 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.