P0671 on GMC
Cylinder 1 Glow Plug Circuit
P0671 on GMC vehicles indicates cylinder 1 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 are small heating elements that warm each cylinder's combustion chamber so a diesel engine can start easily, especially in cold weather. P0671 means the engine computer (through the glow plug control module) detected an electrical fault in the circuit for the cylinder 1 glow plug — typically an open circuit, a short, or resistance that's out of the expected range. The most noticeable effect is harder cold starting, rough running until warm, or increased white exhaust smoke on startup. Typical repair costs on GMC range from $250 to $1,200, depending on the specific model and root cause.
Common Causes of P0671
- •Failed (open or shorted) cylinder 1 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 supply voltage to the glow plug circuit
P0671 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 P0671 across all makes →Frequently Asked Questions
What does P0671 mean on GMC?▼
P0671 stands for "Cylinder 1 Glow Plug Circuit." This is a diesel engine code. Glow plugs are small heating elements that warm each cylinder's combustion chamber so a diesel engine can start easily, especially in cold weather. P0671 means the engine computer (through the glow plug control module) detected an electrical fault in the circuit for the cylinder 1 glow plug — typically an open circuit, a short, or resistance that's out of the expected range. The most noticeable effect is harder cold starting, rough running until warm, or increased white exhaust smoke on startup. On GMC specifically, this code is documented across 1 model.
What causes P0671 on GMC vehicles?▼
Common causes on GMC: Failed (open or shorted) cylinder 1 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 P0671 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 P0671 documented?▼
Au7o has documented P0671 on 1 GMC model: Sierra 3500HD.