LML Duramax: years, specs & known problems

By CarWhere Research · Updated

The LML is the fifth-generation 6.6L Duramax, used in 2011–2016 Silverado and Sierra heavy-duty pickups and identified by an 8th VIN digit of 8. It is rated 397 hp and 765 lb-ft and was the first Duramax with SCR and diesel exhaust fluid. Its best-known concern is the Bosch CP4.2 high-pressure fuel pump.

The LML debuted for 2011 with roughly 60 percent new parts. GM replaced the long-running CP3 pump with a Bosch CP4.2, moved to 30,000-psi piezo injectors, added a ninth injector ahead of the oxidation catalyst for DPF regeneration, and introduced SCR with diesel exhaust fluid, which GM said cut NOx by at least 63 percent. It also brought the first factory exhaust brake to GM trucks and was paired with a strengthened six-speed Allison 1000.

The CP4.2 flows less fuel than the CP3 and is sensitive to poor lubricity, water and contamination; a failure can send metal through the fuel system and take the injectors with it. A class action over the pump (Chapman v. General Motors) settled with final court approval in May 2025 for qualifying buyers in seven states, with GM denying the allegations. Emissions components, especially NOx sensors and DEF parts, are the other common repair area.

LML Duramax at a glance

GM 6.6L Duramax LML V8 turbo-diesel (RPO LML): model years, fuel and peak GM-published output
EngineModel yearsFuelPeak hpPeak torque (lb-ft)Documented problemsRecalls
GM 6.6L Duramax LML V8 turbo-diesel (RPO LML)2011–2016Diesel39776521

CarWhere lists 2 documented problems and 1 NHTSA recall for the LML Duramax, each with a source. Part of the 6.6L Duramax family.

LML Duramax specifications

LML Duramax: design facts (2011–2016)
SpecificationValue
Displacement6.6 liters (403 cu in), 90-degree V8[2]
Bore × stroke103 mm × 99 mm (4.06 × 3.90 in)[2]
8th VIN digit8[2]
Compression ratio16.8:1[3]
Fuel systemBosch common rail with CP4.2 pump and eight piezo injectors at 30,000 psi; ninth injector for DPF regeneration[3]
TurbochargerGarrett GT3788VA variable-geometry; enables the factory exhaust brake[3]
Emissions hardwareDual-circuit EGR, diesel oxidation catalyst, diesel particulate filter, SCR with diesel exhaust fluid (DEF)[3]
NOx reduction (GM claim)At least 63% lower than 2010 models[4]
DEF refill interval (GM estimate)About every 5,000 miles[4]
BiodieselApproved for B20[4]
TransmissionAllison 1000 six-speed automatic, strengthened for the LML's torque[4]

LML Duramax horsepower and torque by year

LML Duramax: GM-published horsepower (hp) and torque (lb-ft) by model year and application
Model yearsApplicationHorsepower (hp)Torque (lb-ft)Source
2011–2016Silverado/Sierra HD pickup397 hp at 3,000 rpm; 765 lb-ft at 1,600 rpm397765[1]
2011Chassis cab and box-delete modelsDifferent EGR system for incomplete-vehicle certification335685[1]

"—" means we could not confirm the figure from a primary source.

Which GM vehicles have the LML Duramax?

GM models and model years offered with the LML Duramax
ModelModel yearsNotes
Chevrolet Silverado 2500HD / 3500HD2011–2016
GMC Sierra 2500HD / 3500HD2011–2016

LML Duramax problems and what to check

CP4.2 high-pressure fuel pump failure (2011–2016)

Major repair

The LML's Bosch CP4.2 pump flows about 20 percent less fuel than the CP3 it replaced and is intolerant of poor lubricity and contaminated fuel. A failure can shed metal into the fuel system and damage the injectors. The Chapman v. General Motors class action (E.D. Mich.) over the pump received final settlement approval in May 2025, covering qualifying 2011–2016 buyers in California, Florida, Illinois, Iowa, New York, Pennsylvania and Texas; GM denied the claims.[3][5][6]

Symptoms

  • Sudden loss of power or stalling
  • Hard start or no start
  • Fuel-rail pressure trouble codes
  • Metal debris found in fuel filter

Check before buying

  • Ask for fuel-filter change records
  • Ask whether the pump has been replaced or converted
  • Avoid trucks with a history of water in fuel

GM program: Chapman v. General Motors settlement (class action; final approval May 2025)

EGR, DPF and SCR/DEF component failures (2011–2016)

Moderate

The LML carries the full emissions stack — EGR, oxidation catalyst, DPF and SCR with DEF — and these components are its most common non-fuel-system repairs. Owners report NOx sensors, the DEF pump and DEF sensors as frequent replacements, especially on early trucks.[3]

Symptoms

  • Check-engine light with emissions codes
  • DEF or emissions warning message
  • Reduced-power or speed-limit mode

Check before buying

  • Scan for stored and pending emissions codes
  • Confirm the emissions hardware has not been removed
  • Ask for NOx sensor and DEF component repair records

LML Duramax recalls

NHTSA safety recalls related to the LML Duramax (campaign numbers link to NHTSA)
NHTSA campaignReportedVehiclesSummary
13V6152013-122012–2013 Silverado/Sierra HD with the 6.6L diesel and dual fuel tanks9,733 vehiclesThe transfer pump that moves fuel from the rear tank to the front tank can malfunction, causing an inaccurate fuel gauge and a possible unexpected stall. Dealers inspect and replace the transfer pump as needed.

LML Duramax issues by model

The same engine shows up on these known-issues pages, with model-specific details.

Related GM research

Confirm a vehicle really has the LML Duramax.

Engine and transmission RPO codes are recorded against the VIN. The CarWhere build sheet decodes a Chevrolet VIN into the factory-ordered option codes on record — engine, transmission, axle and packages. $9.99, instant.

Chevrolet build sheet by VIN

Frequently asked questions

What years is the LML Duramax?

The LML was used in 2011 through 2016 Chevrolet Silverado and GMC Sierra HD pickups. The L5P replaced it for 2017.

How do I tell if a truck has an LML?

LML pickups have an 8 as the 8th VIN digit and RPO code LML on the glovebox label. A DEF filler is another giveaway, since the LML was the first Duramax to use it.

How much horsepower does the LML have?

GM rated the LML at 397 hp at 3,000 rpm and 765 lb-ft at 1,600 rpm in Silverado and Sierra HD pickups.

What is the LML CP4 pump problem?

The Bosch CP4.2 high-pressure pump can fail if fuel lubricity is poor or the fuel is contaminated, sending debris through the fuel system. It was the subject of the Chapman v. GM class action, which settled in 2025.

Does the LML use DEF?

Yes. The LML was the first Duramax with SCR, and GM estimated a DEF refill about every 5,000 miles.

Sources

Ratings are GM-published figures as cited; descriptions are CarWhere’s own summaries of the sources below. Repair costs appear only where a source states them and vary by shop and region.

  1. GM Announces Best-in-Class Power Figures for 2011 6.6-Liter Duramax V-8 Diesel — Cars.com
  2. A Brief History Of Duramax Engine Specs — Diesel Army
  3. Duramax History, Lesson 5: LML — Drivingline
  4. 2011 Chevrolet Silverado HD (GM press information) — Serious Wheels
  5. GM Diesel Fuel Pump Class Action Lawsuit Settlement Final — CarComplaints.com
  6. CP4 Fuel Pump Defect – GM (case page) — Hagens Berman

More Chevrolet tools

Independent reference compiled by CarWhere — not affiliated with or endorsed by General Motors. Chevrolet, GMC, Cadillac, Corvette, Duramax, Vortec and the model names are trademarks of their owner.