LMM Duramax: years, specs & known problems

By CarWhere Research · Updated

The LMM is the fourth-generation 6.6L Duramax, used in 2007.5–2010 Silverado and Sierra heavy-duty pickups and identified by an 8th VIN digit of 6. It is rated 365 hp and 660 lb-ft and was the first Duramax with a diesel particulate filter, which is where most of its ownership issues come from.

The LMM launched with the new GMT900 Silverado and Sierra HD for the 2007.5 model year to meet 2007 emissions rules. The core engine stayed close to the LBZ, with the same CP3 pump, 26,000-psi solenoid injectors (now six-hole) and Garrett variable-geometry turbo, but GM added a larger EGR cooler, a diesel oxidation catalyst, a diesel particulate filter and an intake throttle valve, and paired it with the six-speed Allison 1000.

The DPF needs active regeneration roughly every 400 miles, during which extra fuel is injected to burn off soot. That costs fuel economy and can dilute engine oil, and the EGR cooler can plug, crack or leak. Coolant loss is often the first warning sign, so service history and an emissions-system scan matter more on an LMM than on earlier Duramax engines.

LMM Duramax at a glance

GM 6.6L Duramax LMM V8 turbo-diesel (RPO LMM): model years, fuel and peak GM-published output
EngineModel yearsFuelPeak hpPeak torque (lb-ft)Documented problemsRecalls
GM 6.6L Duramax LMM V8 turbo-diesel (RPO LMM)2007.5–2010Diesel36566030

CarWhere lists 3 documented problems and 0 NHTSA recalls for the LMM Duramax, each with a source. Part of the 6.6L Duramax family.

LMM Duramax specifications

LMM Duramax: design facts (2007.5–2010)
SpecificationValue
Displacement6.6 liters (403 cu in), 90-degree V8[3]
Bore × stroke103 mm × 99 mm (4.06 × 3.90 in)[3]
8th VIN digit6[3]
Compression ratio16.8:1[1]
Fuel systemBosch common rail with CP3 pump, 26,000 psi; six-hole solenoid injectors outside the valve covers[1]
TurbochargerGarrett GT3788VA variable-geometry[1]
Emissions hardwareLarger cooled EGR, diesel oxidation catalyst, diesel particulate filter (first Duramax with a DPF), intake throttle valve[1]
DPF regenerationActive regeneration roughly every 400 miles[1]
TransmissionAllison 1000 six-speed automatic[2]

LMM Duramax horsepower and torque by year

LMM Duramax: GM-published horsepower (hp) and torque (lb-ft) by model year and application
Model yearsApplicationHorsepower (hp)Torque (lb-ft)Source
2007.5–2010Silverado/Sierra HD pickup365 hp at 3,100 rpm; 660 lb-ft at 1,800 rpm365660[1]
2007.5–2009Kodiak/TopKick (LYE option)330620[2]

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

Which GM vehicles have the LMM Duramax?

GM models and model years offered with the LMM Duramax
ModelModel yearsNotes
Chevrolet Silverado 2500HD / 3500HD2007.5–2010
GMC Sierra 2500HD / 3500HD2007.5–2010
Chevrolet Kodiak / GMC TopKick2007.5–2009Medium-duty LYE and LRX options with lower ratings

LMM Duramax problems and what to check

DPF regeneration, fuel economy and oil dilution (2007.5–2010)

Moderate

Active DPF regeneration injects extra fuel to raise exhaust temperatures above 1,000°F, roughly every 400 miles. It is the main reason the LMM gets lower fuel economy than earlier Duramax engines and is linked to diluted engine oil; early DPF units were also prone to cracking and leaking.[1]

Symptoms

  • Frequent regenerations on short trips
  • DPF or exhaust-pressure warning messages
  • Engine-oil level rising

Check before buying

  • Scan for DPF and exhaust-pressure codes
  • Confirm the original emissions hardware is present and working
  • Check oil level and condition

EGR cooler plugging or leaking (2007.5–2010)

Moderate

The LMM's larger EGR cooler can plug with soot, crack or leak coolant into the exhaust side. Unexplained coolant consumption is often the first sign.[1]

Symptoms

  • Coolant loss without visible leaks
  • White smoke with a sweet smell
  • EGR flow trouble codes

Check before buying

  • Watch the coolant level over a test drive and cool-down
  • Ask whether the EGR cooler has been replaced

Cracked pistons on modified engines (2007.5–2010)

Minor

The LMM shares the LBZ's pistons, which can crack across the wrist-pin centerline, usually only above about 650 rear-wheel horsepower with tuning.[1]

Symptoms

  • Misfire
  • Heavy blow-by

Check before buying

  • Ask about tuning history
  • Check blow-by at the oil fill

Related GM research

Confirm a vehicle really has the LMM 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 LMM Duramax?

The LMM was used in 2007.5 through 2010 Chevrolet Silverado and GMC Sierra HD pickups, starting with the new GMT900 body.

How do I tell if a truck has an LMM?

LMM trucks have a 6 as the 8th VIN digit and RPO code LMM on the glovebox label. Any 2007 HD in the new body style with a Duramax is an LMM; 2007 Classic models have the LBZ.

How much horsepower does the LMM have?

GM rated the LMM at 365 hp at 3,100 rpm and 660 lb-ft at 1,800 rpm in Silverado and Sierra HD pickups.

Does the LMM have DEF?

No. The LMM has a diesel particulate filter and EGR but no SCR system, so it does not use diesel exhaust fluid. DEF arrived with the LML for 2011.

What are common LMM problems?

Most issues trace to emissions hardware: frequent DPF regenerations, oil dilution, early DPF cracking and EGR cooler leaks.

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. Duramax History, Lesson 4: LMM — Drivingline
  2. Duramax V8 engine — Wikipedia (secondary reference)
  3. A Brief History Of Duramax Engine Specs — Diesel Army

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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.