P0671 on Mercedes-Benz: How to Diagnose & Fix
Cylinder 1 Glow Plug Circuit
1 Mercedes-Benz model · 1 documented issue · $300-$1,500 repair
P0671 on Mercedes-Benz by model: symptoms, diagnosis and fix
Sprinter glow plugs fail with age, causing hard starting in cold weather, rough idle when cold, and white smoke on startup. The OM642 V6 is particularly prone to glow plug seizure in the cylinder head, making removal difficult and risking broken glow plugs that require cylinder head removal to extract.
Common Symptoms
- Hard starting in cold weather
- Extended cranking before engine fires
- Rough idle for first 30-60 seconds when cold
- White smoke on startup
- Glow plug warning light staying on
How to Fix
Replace all glow plugs as a set. Apply anti-seize compound to new glow plug threads. On the OM642, use penetrating oil on the glow plugs and allow it to soak before removal to reduce seizure risk. If a glow plug breaks during removal, specialized extraction tools are available before resorting to head removal.
Owner tips & cautions
- TipReplace glow plugs proactively every 80,000 miles before they seize. Apply anti-seize compound generously. A broken glow plug extraction on the OM642 can cost $1,000+ in labor alone.
P0671 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 P0671 mean on a Mercedes-Benz?
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 Mercedes-Benz it is documented across 1 model: Sprinter.
What are the most common causes of P0671?
The most common causes of P0671 are: 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. The specific cause varies by vehicle.
How much does it cost to fix P0671 on a Mercedes-Benz?
Published repair estimates on Mercedes-Benz range from $300 to $1,500 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 P0671 on a different make?
View P0671 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.