P0678 on Chevrolet: How to Diagnose & Fix
Cylinder 8 Glow Plug Circuit
1 Chevrolet model · 1 documented issue · $300-$1,800 repair
P0678 on Chevrolet by model: symptoms, diagnosis and fix
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.
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
P0678 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 P0678 mean on a Chevrolet?
P0678 stands for "Cylinder 8 Glow Plug Circuit." A fault in the glow plug/heater circuit for cylinder 8. The control module detected an open or short in that individual glow plug circuit. On Chevrolet it is documented across 1 model: Express.
What are the most common causes of P0678?
The most common causes of P0678 are: Faulty cylinder 8 glow plug, Open or short in the glow plug circuit, Corroded/damaged connector, Wiring damage, Glow plug module fault. The specific cause varies by vehicle.
How much does it cost to fix P0678 on a Chevrolet?
Published repair estimates on Chevrolet range from $300 to $1,800 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 P0678 on a different make?
View P0678 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.