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P0671MinorEngine

P0671: How to Diagnose & Fix — Cylinder 1 Glow Plug Circuit

4 vehicles · 3 makes · $200-$1,800 repair

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How to diagnose and fix P0671: most-reported vehicles

Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.

Mercedes-Benz Sprinter · 2007–2025

Community reported
1,500 owners
Link to this issueError Codes:P0671P0672P0673P0674P0380

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.
Typical repair cost:$300 - $1,500

Research This Issue

Based on 1,500 owner reports

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Community Reported
High Confidence1,500 owner reportsLast reported by owners Jan 2026Reviewed Mar 2026

Chevrolet Silverado 3500HD · 2001–2020

Community reported
250 owners
Link to this issueError Codes:P0380P0671P0672P0673P0674

Glow plugs fail causing difficult cold weather starting. Can also swell and break during removal, requiring extraction. Glow plug module can also fail.

Common Symptoms

  • Hard starting in cold weather
  • Extended cranking
  • White smoke on cold start
  • Glow plug indicator stays on too long
  • Rough idle when cold

How to Fix

Replace failed glow plugs. Use penetrating oil and heat to prevent breakage during removal. Replace glow plug controller module if diagnostics indicate module failure.

Typical repair cost:$200 - $800
Sources for this issue (1)
  • GM Special Coverage N212338290 - Glow Plug Failuretsb

Research This Issue

Based on 250 owner reports

GoogleRedditYouTubeNHTSA
Community Reported
Low Confidence250 owner reportsLast reported by owners Mar 2026Reviewed Mar 2026

GMC Sierra 3500HD · 2007–2019

Community reported
110 owners
Link to this issueError Codes:P0670P0671P0672P0673P0674P0380

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).

Typical repair cost:$250 - $1,200
Sources for this issue (1)
  • NHTSA Campaign 21V504 - Roof-Rail Airbag Inflator Rupture Recallrecall

Research This Issue

Based on 110 owner reports

GoogleRedditYouTubeNHTSA
Community Reported
Medium Confidence110 owner reportsReviewed Apr 2026

Chevrolet Express · 2011–2016

Link to this issueError Codes:P0670P0671P0672P0673P0674P0675P0676P0677P0678

The 6.6L Duramax LGH offered in Express 2500/3500/4500 vans from 2011 to 2016 has a well-documented glow plug system weakness. Individual glow plugs fail open, and the glow plug control module itself develops open-driver and no-power-to-glow-plug faults - a failure mode common enough that specialist board-repair houses list the 2011-2016 Chevrolet Express 6.6L LGH GPCM as a standing repair line. GM issued a service bulletin covering 2011-2012 Express vans with the LGH and LML Duramax where the malfunction indicator lamp illuminates for glow plug faults; the bulletin notes there is usually no drivability complaint in mild weather, but harder cold starting may be present. In practice owners in cold climates get extended cranking, white startup smoke and a rough first minute of running, plus a persistent MIL that will fail an inspection. Do not confuse this with the 2023+ Express, which uses the completely different 6.6L L5P Duramax and whose injector-related complaints are their own story.

Common Symptoms

  • Malfunction indicator lamp on with glow plug circuit codes
  • Extended cranking in cold weather
  • White smoke on cold startup
  • Rough running for the first minute after a cold start
  • Wait-to-start behavior that never satisfies

How to Fix

Scan for the specific glow plug circuit code to identify which cylinders report open, then load-test each glow plug individually - a single open plug sets the light, so replacing the module first is a common misdiagnosis. If the module reports open drivers or no output at all, the GPCM is at fault and can either be replaced new or sent for board-level repair at a fraction of dealer cost. When multiple plugs test bad, replace the full set; mixing old and new plugs invites a repeat visit. Access is tight - budget significant labor, particularly on the driver's side in the van body. No recall covers this; the GM bulletin is a service bulletin only.

Typical repair cost:$300 - $1,800
Sources for this issue (3)
  • 2011-2016 Chevrolet Express 2500/3500/4500 6.6L Duramax LGH Glow Plug Control Module Repair - documented failure modes: no power to glow plugs, open driver errorsarticle
  • $4,000 Duramax glow plug problem "not uncommon" per Chevrolet Customer Service - Chevy and GMC Duramax Diesel Forumforum
  • Glow plugs going bad - Chevy and GMC Duramax Diesel Forumforum

Research This Issue

GoogleRedditYouTubeNHTSA
Community Reported
Medium ConfidenceVerifiedReviewed Aug 2026

Find P0671 by make

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Chevrolet · 2 issuesGMC · 1 issueMercedes-Benz · 1 issue

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?

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.

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?

Repair costs for P0671 range from $200 to $1,800, depending on the vehicle and root cause.

Which vehicles are affected by P0671?

Au7o has documented P0671 across 4 vehicle models from 3 manufacturers: Chevrolet, GMC, Mercedes-Benz.

Related codes

  • P0670 · Glow Plug Module Control Circuit
  • P0672 · Cylinder 2 Glow Plug Circuit
  • P0673 · Cylinder 3 Glow Plug Circuit
  • P0674 · Cylinder 4 Glow Plug Circuit
  • 00522 · Engine Coolant Temperature Sensor (G62): Open Circuit / Short to Positive (B+)
  • 16500 · Engine Coolant Temp. Sensor (G62): Implausible Signal
  • 16502 · Engine Coolant Temperature Sensor (G62): Signal too High
  • 16566 · Mass Air Flow Sensor Signal Too Low (VAG)
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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.

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